There are only so many moves that are available to him. It has been reported that he's not able to work with very many teams which is why he keeps going back to the Cardinals to make deals. He is financially strung by the models and/or JH so the best FA's will never come here long term. At some point, he'll run out of prospects to deal (Sox already ranked 14th on BA).
If there's a plan B, it probably isn't as good for 2026-7 as Bregman would have been. I don't think the Bregman deal would have been a slam dunk to work out, but we were told that the Sox are in a WS contention window right now. If so, they aren't acting like it.