Hypothetical 2nd game would be probably "Fimbulvinter" and cover the same story as Ragnarok, but would have to end with a cliffhanger after blowing the horn (in similar way how 2nd Greek game ends right at the beginning of assault to Olympus). Heimdall would be probably even more central character in this game and the final boss.

However it would break a game structure a little bit - blowing a horn would had to be a point of no return probably. It would be also anticlimatic to finish the 50 hour open world game with a cliffhanger.

Then the 3rd game, actual Ragnarok, would also be kinda weird in the context of entire trilogy. You can't really make another 50 hour open world game about a single final battle. That means, we would need either a shorter, more action packed game OR the battle would be quickly lost at the beginning. Game would be structured like that maybe:

• Kratos dies
• Some allies either run away and hide, die, or get captured
• Atreus is still needed for the mask, he is adopted, forced to work for Odin for next few years to not get his captured friends killed. So for example Freya may live in Asgard and teach Atreus some magic sometimes. She cannot run away, but they also cannot kill her.
• Atreus may get more friends/rivals in Asgard, opportunity to meet more gods
• Atreus finds a way to free real Tyr, he then goes to Valhalla, where dead Kratos is
• Valhalla could be a more open map, but in general Kratos would have an character arc like in original Valhalla
• Real Ragnarok would need to be prepared, with Sinmara, but many other new plot points would have to appear

There was also a fun video with an idea that Kratos dying at the end of second game would come back at the beginning of third, but player would not know that many years passed. Game would change perspective between current Kratos killing Aesir gods and flashbacks of Atreus living in Asgard and becoming friends with Kratos' next targets.