I don't understand the talk about tre, he's on contract and he's a really good back up imo. We can disagree on this point but that's not the debate.
About Mamu it's different, he was a clear goner a few weeks ago but he's a real basketball player, despite some physical limitations so he could have his place with the team.
But the Spurs will have to cut/don't ressign some players and make some choices : barlow is gone imo so is graham, then you have mamu, osman, bassey and maybe wesley.
IMO the others are not in danger except if there's some trades : Wemby, Vassell, Sochan, Jones, Johnson, Champagnie, Branham, Collins, Cissoko, that's 9 players and if you count on like 2 rookies you only have four roster spots left.