MELTA BOMBS
...
Assault
-Unless used in assaults against vehicles, gun emplacements, or Monstrous Creatures, melta bombs have no effect
*emphasis mine
Seems pretty clear-cut to me (at first).
Then again, you
were in assault with
MCs. If they were vehicles (walkers), then I would say absolutely no way they carry over b/c rolling armor penetration =/= rolling to wound. However, since you did roll to wound and caused more wounds than the
MCs initially had, I guess they should carry over.
Goofy either way, but I would
RP this as the character's creations exploding and falling on top of him. Plus a whole mess'o destruction-crazed boyz ain't gonna care who gets a little collateral damage.