Both gods fall on the snake, on top of which there would be a brief "semi-playable" confrontation. It would be very rough as it begins to stumble trying to regain mobility; jumps, falls and unsteadiness everywhere. Ending with the contenders landing on one of the huge spikes embedded in the wall.

It can be seen how Jörmungandr is already regaining full mobility. So Kratos, observing where they have fallen, has an idea: "The snake could help us with the wall!" he shouts to his son, who continues on the snake's head, pointing to the big spike slyly.

But right after that, Thor catches Kratos off guard by momentarily disarming him and cornering him against the wall. As the god of thunder is about to deliver the hammer coup de grace, the serpent can be seen lunging at his back. As Atreus vocifies "No! Now, father, jump!".

The snake bites and pulls out the spike from the wall on which Thor continues, while Kratos manages to evade the attack and dives into the void.

Immediately we would take control of Atreus, who with his powers, shining his eyes and shouting words in ancient language gives indications to Jörmungandr. So, the player now takes direct control of the snake, although in a very brief and limited way. Practically like a minigame.

 The goal is to quickly insert the giant spike right into the wall flaw (the mechanics could become similar to the chisel that opened magical doors in the previous game) before Thor can counterattack by overloading his lightning bolts.

Atreus jumps at the last moment, before drilling into the rock. The wall cracks with a loud noise. The impact is such that the snake pierces through it, getting lost under the collapse of the huge boulders of the falling wall.

A breach in the wall finally opens up, which seems to leave a clear path. Apparently, both Thor and Jörmungandr remain under the rubble.

The action follows Atreus, who cannot find his father who had fallen a little further away, nor can he see much amidst all the dust and debris. He advances a little through the hole and sees a shadow approaching him from the other side.

Note about bosses: In this epic final chapter of Ragnarök, there would be two types of boss fights: the traditional ones in "arenas", which would be mostly almost identical to the ones in the game, and the more "moving" ones that would be complete levels of their own with their appropriate stage. The last are the ones we are concerned with in this case.
They would be quite cinematic or could even become "puzzle boss" style. Player agency would be limited while providing mechanics unique to these battles, in pursuit of spectacularity. To get an idea of what they would be like, there are several moments in the game itself, such as the very beginning attacking Freya or the rescue of Freyr, both scenes with simple interactive mechanics and spectacular cutscenes. Or even in the previous videogame in the excellent and epic final battle against Baldur, with Thamur controlled by Freya in between (it is a crime that no situation or boss is even close in scale and dizziness to this one in its sequel, not even in the great final war...). That's the idea.
Also, in several of these fights, as the action and narrative progressed, control would dynamically switch from Kratos to Atreus often, according to suitability.
However, one point must be clear: the fact that these levels are more cinematic does not mean that the other more traditional battles (with feet on the ground and full control of the character) were not at least slightly challenging. As the real final bosses deserve. Not a simple walk that you beat by mashing a button, as they are in the game.

In this version, the scene of Thrúd and Sif took place after the demolition of the wall and not before, but it would be nearly identical to the original. Except for the presence of Sindri and a couple of details that would be modified. Such as Thrúd would appear among the dust of the collapse and the whole place would be in ruins; she would be visibly even more pissed off because her father had just been defeated; Sif and Skjöldr would also appear among the dust that does not allow a good visibility; plus these two would go, unlike in the original material, out of shot on the opposite side of the screen to where they appeared (both modifications trying to soften the "theatrical feel" I mentioned in the preface); including certain lines of dialogue to adapt all this.

As for example: Thrúd would reply to her mother "But they just...!". Sif would interrupt her by assuring "You know that's not enough to finish your father off. I can feel his heartbeat... in the ends of my hair. He still has a war to wage, at least for the moment...". Then she tells her daughter to go with them, as he’ll listen only to her.

Note about Sif: This "power of Sif" I have pulled it out of my sleeve, I admit it. Even so, I'm going to justify myself hard: Because she is supposed to be the goddess of fertility, harvests, fidelity, family, marriage... (I mean, a whole bunch of stereotypes acquired, just for a change, by the female divinities of mythologies that are not so sexist...). Her hair is supposed to represent the wheat fields and how she is connected to nature and trees. Some kind of an earth goddess, in a nutshell. So it might make sense that she would have certain supernatural bonds or links to living beings, such as the ability to sense them. Also, her name is etymologically related to the word 'sib' which refers to kinship, affinity or connection.
So... why not?

The scene ends with Thrúd finally convinced of her grandfather's wickedness and joining the group of attackers.
Right after that Kratos would finally appear, whom we would take control of once again, followed by conversations in much the same way as in the game.

When they manage to gain some ground and are staying on the edge of the area in ruins, they observe how on the horizon, along the main street in the background, the road is cut off by a horde of Einherjar. Commanded by Odin on horseback escorted at the same time by another man of large size. The battle has only just begun...

Note: Putting such a challenge to be overcome by father and son almost single-handedly, outnumbered a priori, might indeed give more sense to the warning that Freya previously makes during the scene "Open your heart" to Kratos : "You going alone, it's suicide". 

Note: Sleipnir, Odin's octopedal horse, might make a prior appearance in the game, albeit in passing. As well as Thor's goats.

VIDAR

Oh, by the way, the one accompanying Odin is Vidar (Viðarr). The inclusion of he turned out to be the most drastic and notorious change in this project, as it would considerably change the previous content of the game. But as I will explain below there is a good reason besides that it would not be overly complex to place or adapt.

Just as the rest of the characters in the game are not presented exposing their background in the Norse myths, with this one there would be no exception.
But in this case, I can give him some context by exposing what Mimir might have told previously in the game regarding what he knows about this Aesir, as Atreus asks him about him after returning from one of his trips to Asgard:

–Mimir, who is the huge, quiet guy who is always standing still in front of Odin's study door? It's almost as if he wasn't there, like another piece of furniture in the house. Even the rest of the aesir advised me to pretend he wasn't there. Ignore him... –Atreus would ask curiously.

–Aaah... Vidar The Silent. The other bastard son of Odin besides Thor. Only... this time with a different giantess: Gridr. For not liking giants, the All-Father sure did take them to bed whenever the depraved old man could!
Anyway, as for Vidar, or the God of Silence as some call him, no one knows much about him, other than his immense devotion and loyalty to his father. Besides, some say he could be as powerful as his brother Thor. But his muteness and impassivity make him the most reserved and mysterious Aesir. He is like Odin's watchdog.

–Literally... –Atreus would interrupt.

–If you ask me about his mutism... knowing Odin, I would venture to say that it was he himself who cut off his tongue so that he would be as submissive as possible and would not question him. –Mimir would conclude.

Note: If you are not familiar with this mythological character, I invite you to research and read about him at the end of this reading because it is very curious how timely he has been for this project and how interesting he would have been for the game. Also, I will add at the end another note as an anecdote of how I came up with the idea of introducing Vidar in this project and how it worked as a trigger or motivation to finally do it.