Unless a team that trades for him has a "wink-nod, off-the-record understanding" that he’ll get a deal he wants at the start of the next off-season.
I don't view the NFLPA agreeing to keep the franchise tag as either greedy or stupid. The tag affects at most 32 players in the entire league each season. Demanding it disappear would require the union to give up something in return, like agreeing to a lower overall cap number, a lower minimum salary, etc., which would negatively affect far more members of the union. Hurting most of the rank and file to benefit a few of the elite members of the union would to me be very irresponsible of the NFLPA leadership. If the union members are smart they'll tell their reps that they're perfectly okay with negotiating to keep the franchise tag, but in exchange getting better post-career health care coverage, guaranteed contracts, higher minimum salaries, or other things like that. Everyone is so shocked that the Steelers players have said out loud how much they resent Bell not showing up, but that doesn't mean that the same resentments of extremely highly-paid WRs or RBs by linemen don't exist on every team. None of those guys get a fraction of the salary they actually get without a stout offensive line opening holes and giving the QB time to throw, yet relatively speaking the linemen are grossly underpaid. I'd bet all of them think it's ridiculous when a running back cries over "only" getting offered a two-year guaranteed contract averaging more than $15 million a year. A franchise tag means absolutely nothing to them.
I was quoting Mike Florio over at ProFootballTalk. He stated in the scenario of a wink-nod, off-the-record agreement both parties would have an understanding of "key terms" of a contract offer on a hypothetical table after the season concluded. Florio also stated an arrangement like that is unenforceable and a violation of the labor deal, but these sort of deals do occasionally occur. I'm not saying Bell is getting traded, but it may happen with a team having a wink-nod off-the-record arrangement with LeVeon Bell's agent for a long-term deal in January.