The debt is that this guy owes money. If he has it or not he still owes it.
He will burn in hell / or may come back as a gillgul cause he owes money.
Now if your mochel, it is a complete present.
I think one can be mikadesh a ishah.... let me check
המקדש במלוה אינה מקודשת
Rambam does pasken Mecher is chal, but that's it's own mystery.
Also it's quite possible he doesn't personally owe anything.
Confused as to the relevance
in a case where beis din compelled someone to give tzedaka, it was not given out of goodness of heart, yet clearly it counts as Masser.