Just a thought for Necromancy skills and if the summon undead *would* require bodies:
They could add in a second skill that would be able to target those ash piles/heavily damaged corpses, and instead of summoning a zombie/skellington, summon some form of spirit/ghost.
I don't know if they need to make a separate skill. Just make it so a raise zombie skill will raise an ash zombie/spirit if targeting an ash pile, or an ice zombie if targeting ice remains, etc. So it would still kind of have that elemental flavor that summoning has, but through the use of dead enemies, which would largely depend on the nature of your party. If you have a pyro, you'll get a lot more ash zombies, for example.
Each zombie can have different stats and abilities. Ash zombies would be extremely vulnerable to air probably (just blow them away), and maybe they could have a skill that would let them spray themselves at a group of enemies, destroying the summon but blinding the enemies. Stuff like that.
