It would be nice to know Bob, Emilio, and Roscoe have the option to come back if they so desire. I generally don't believe in entitlements, but after each of them put in at least four decades on the show, you'd think they would have at least the SMALLEST say in if they want to continue.
They're fortunate enough to have other extraneous activities to keep them from sitting home and doing nothing. Book signings, personal appearances, etc.
Plus, like Bob, who does a telethon in Canada every year, Sesame has generated enough goodwill to keep him relevant there, if not on the Street.
If it's in their fate to come back, great, hopefully no hard feelings.
If any of them decide to walk, like Joey did, who could blame them?