I don't know if you've thought about this, but once Tony found out Vanessa was dating Justin his life was over anyway, so he was doomed whether Vanessa accidentally killed Tony or not.
This take is very surprising to me (I know it's a 15 years old comment but I only recently came to this forum): why would tony end up being killed, once he found out about vanessa dating justin? Especially with his connections to the mob I don't see why vanessa (who's ofc physically much weaker) or justin would want to make such powerful enemies.