Instead of being executed, he was/found a way to get locked up in Coruscant prison.
When Boba Fett is arrested, Slick is the one to save him from getting executed/sent back to the Kaminoans. Somehow.
Slick is also the one to save Dogma from getting decommissioned or reconditioned, instead gaining a prison mate.
Boba has some sort of familial relationship with them, if only because of proximity.
Slick and the Coruscant Guard have some sort of understanding. (This is a different post about my au that will eventually exist).
Dogma doesn’t really warm up to Slick until he gets news of what happens to Tup and subsequently, Fives.
All three of them survive, and later have varying levels of closeness with Rex and “others”.
There’s more, but that’s a different post. This stuff can pass in canon. The rest are more… au-esque.