Ok, everything launched, blown apart, dropped, shot Etc. etc.... Will have it's own innate vector, a expanding sphere surrounding the entire volume where combat took place. Thus the miniscule probability of another ship encountering said debris is so low that even insurance actuaries would probably ignore it (Counts as an Act of God). Plus factor in that any potentially ship damaging debris would be fully visible with ship's sensors. It really comes back to the 1st line of this reply, Space is REALLY Big.