There's very, very, very few players in the league that are truly off the table irrespective of the offer being presented. Of about 400 NBA players, I'd dare say less than 30 (maybe less than 20) are actually off the table, non-starter kind of protected. For everyone else, it'll always depend on the offer - even such a promising talent as SGA wasn't off the table when the right deal came through.
Having said that, I would really hesitate to trade either Keldon or Samanic unless we're talking about a king's ransom. Every other player on our team either has a roleplayer ceiling with no clear flashes of star potential (Vassell, White), has potential but hasn't so far been able to consistently translate it to the court (Lonnie, though in a pinch he'd be the third name on my do-not-trade list), or has real value but would be better served traded for assets (I'm still convinced we gotta sell high on Dejounte before other teams start scouting him out of games).