Ending B: The Original Version
So you may have read in the trivia section how the "Kill Michael" ending would've originally turned out: if you choose to have Franklin save Michael as he's dangling off that chimney, Franklin then sacrifices himself. Mike and Trevor make amends and go kill Steve Haines, then Trevor offs Devin Weston, and Michael is blamed for Franklin's death by his friends.
That could've worked as an alternate ending. Then either have Lamar take Franklin's place or just play free roam as Michael or Trevor.