One possibility is treating the game like scaffolding. It feels like textures and images could all be replaced fairly easily with generative versions. Toss them in Midjourney with /describe, play around to create replacements. Or Stable Diffusion or whatever. (Not sure how many things are "images" and how many are other structures like shaders.)
Maps are harder, at least I imagine harder to deconstruct into atomic pieces that can be replaced. Though it's interesting to think about whether an LLM could decompose them into more semantic pieces, if it could understand the underlying structure that may only have existed in the mind of the original map creator.
I imagine things like quests, stats, etc., would all be amenable to generation.
Maybe the big question is if things really are separable enough to use the old game as scaffolding: can you replace 10% of the game, or 50%, or 90% and have a meaningfully playable game?