Would the world be so different, he wouldn't even recognize it?
And what if ripples from one of the many changes he made led to changes that caused the Quantum Leap project to never have begun. Do all his good deeds get wiped out then. Oh you time travel paradoxes. You make my noggin befuddled!
There was a leap which caused Al to never be on Project Quantum Leap (Two actually!) and Roddy McDowell took over the role of holographic projection that only Sam could see and hear.
Sam remembered Al though and so worked to put right what once went wrong and got Al back onto the team.
That was until he told Al's first wife to wait for him to return from the war - but we will never know what happened after that as it was the last episode.
I like to think there is a little of Sam inside us all.
Actually it wasn't that Al didn't get on the project, that was caused because Sam caused Al to be executed by telling his girlfriend not to go to the CO and risk her career by alibiing him.