In a keeper league, if you're eliminated, then any player you cannot keep is worth literally nothing to you, and it is a positive-value move to trade them for anything that isn't worth literally nothing to you. If the best you can get for Breece Hall is a conditional pick-swap in the 22nd-round (or whatever the last round in your draft is), then trading Hall for a future pick swap makes your team better in expectation. That's a +EV move for you and you "should" make it.
The relevant question isn't "what is Breece Hall worth". He's worth literally zero. The relevant question is "what is the absolute most I can get for him".
Of course, a "Hall-for-pennies" trade will probably make your leaguemates very mad. The five playoff teams who didn't get Breece Hall for virtually nothing are going to be quite upset that one of their competitors got a huge upgrade at no cost. The solution here is for them to offer you more than a 22nd-round draft pick for him. If they don't want their competitor to get Breece for nothing, they should offer more than nothing. If they're unwilling to offer more than nothing, then they lose the right to complain about someone else offering nothing. It's not your job to maximize their championship odds, it's only your job to maximize *your own* championship odds.
Now, this is the sort of obviously correct move that might not be worth the heat. Trading Breece for whatever you can get is indisputably the right move for your team, but you might very reasonably decide it's not worth upsetting league dynamics for such a pathetic payoff. That's fine-- I wouldn't do it, either. "Not having to listen to my leaguemates yell at me" is worth more to me than a slightly better last-round pick.
But if I knew my league well enough and knew it wouldn't ignite a firestorm, I'd be pretty up-front-- "I'm not making the playoffs and I can't keep Breece Hall, so his value to me is literally zero. As a result, I will trade him for something whose value to me is more than literally zero, and my team will be better as a result. I encourage everyone to make an offer and I'll go with whatever offer is best for my team-- because my concern is making my own team better. If anyone is upset that I let him go for too little, please remember that you are free to offer more. If you don't offer more, then you implicitly agree he wasn't worth more, and therefore it shouldn't be surprising that he didn't fetch more." Most of my leagues aren't the sort of leagues where this would fly-- we're mostly just old friends playing for fun. But in super competitive leagues, this sort of thing should be seen as above-board.
(If your league doesn't allow trading future picks, trading for players is the same basic idea. Anyone you get who improves your keepers-- no matter how marginally-- is worth more to you than Hall, who has no value to you at all.)
Again, the question of what's the optimal play (getting absolutely anything at all) is separate from the question of what's the "right" play-- you do need to keep in mind league dynamics. It's not worth pissing everyone off for pennies.