I might be misunderstanding the motivations on various ends, but it seems like the relevant question is why the Twins continue to be involved. My initial reaction was that the trade worked out fairly well for both the Dodgers and Twins, whereas the Red Sox took a safer, already established MLB player and were content to dump as much salary as they could.
I can't imagine that the Dodgers would replace Graterol with May, unless Price is no longer part of the deal or something (even if Boston paid more, which doesn't make sense for them because the whole point is to use Betts' value to get out from under the tax threshold, I don't think the Dodgers would budge on May). But it seems like they could get something close to the original deal done by including Gonsolin, which was/is one of the bigger rumors out there.
The question would then become whether or not the Dodgers definitely want to pivot to moving Maeda, since the Twins component of the deal isn't necessary to get the deal for Betts done. It's possible that LA could just want Graterol, and I guess maybe an additional piece, but surely the contingent Pederson deal is more important for the Dodgers' own tax purposes.
I guess maybe an alternative would be that the Twins give up a different prospect or two who would go to Boston, but that seems like more of a stretch. My read/guess is that if the deal isn't going to fully collapse, then it's more likely that either two distinct deals will occur, or the Twins won't end up with Maeda. I guess it might be a little weird for LA to keep Maeda at this point, but who knows.