Welcome, Nick V! Glad you liked "Mean Streets." I'd give it 10 out of 10, but that's one man's opinion. It looked to me as if all of them in Tony's car were alive at the end (and being led away to an ambulance). I think the point there was not whether they lived or died, but that Michael was able to attack them without fear of Charlie's uncle Giovanni.
The scene in the back of Tony's car is one of the best ever to appear in a Scorsese film--it has that ad-libbed quality that makes his films so realistic and natural. That doo-wop sound track is wonderful, too. IMO, it was Keitel's greatest performance, and DeNiro's second-greatest (after "Raging Bull").
BTW: the actors who played Michael (Richard Romanus) and Tony (David Proval) turned up on "Sopranos": Romanus was Melfi's ex-husband, Proval was Richie Aprile. The shooter in Michael's car at the end of "Mean Streets" was Scorsese himself.