Injuries are random in real life so I support some type of randomized injury type/length system. However, I think we should determine how often said system is ran. I think the game is more challenging creatively if we don't use injuries to explain Japan tours. That's lazy booking.
I agree with Dylan, that retirements are never permanent, unless career ending (Magnum). Maybe a maximum age limit? They could still be used seconds, referees, angles, but no matches.