Well I just wanted to know if the same thing happened in New Vegas, but it mainly happened with the raiders remember the Bethesda Ruins the highway by Vault 101, also you know that super mutant camp by Rivet City right across the way from Project Purity the mutants turned to goo and ash piles there too. Remember this is on the Xbox 360 version.
Alright I completed my test at Bethesda Ruins not to long ago and this is how it went.
-I counted and killed 7 raiders in just the exterior area and 3 were goo/ashified
-when I returned ( around 4 in game days later) I counted and killed 7 raiders total in the same exterior area (and in the same spots as last time)
Ill continue to keep an eye out for this happening but as it would seem (and Im not saying you're not having the problem) I don't see the goo/ash=no respawns for me. :shrug: (just to make this clear I did do my test on the xbox with GOTY edition)
One thing I did notice though that could explain it is that the goo/ash piles do not go away. Is this what you are referring to? Prehaps you are seeing these piles and assuming that what originially made them did not respawn? just a thought.