I'd probably make an all new engine as I'm more interested in making a metroidvania style game than a roguelike and AVWW has a lot of cool spells, effects, terrains, enemies and the time tears themselves that I can get pretty creative with... including the settlement building, rescuing survivors, stealth missions, Power Legs, monster timezone migration based on beating lieutenants, a freefall scene, a volcano escape, stealing material from a tech base (ehhh, that might have been the second game)
I don't even have to steal assets - the CORE mechanics I'm interested in borrowing is basically the time mechanics and the spellgem mechanics.
EDIT: And I never even got a Legendary Acid Gills on my playthroughs