His current level of performance is not mediocre (.875 in last 14 days). And neither is .780. Yeah, that still makes him a net negative player but that's always been the case. Question is can he actually do that. If the trend of hard-hit and well-hit balls over the past six weeks that has finally brought him to this point continues, he can. If he has too many ABs like yesterday, no. What we know for sure is he isn't going anywhere and current team is working just fine.
Soto has options and is definitely the guy I would replace at the trade deadline but I don't think they are going to make any of these moves until after the All-Star break.
I also don't think Sosa is going to take away playing time from Merrifield specifically once Marsh returns, there's just so few opportunities for either of them to play the IF once Turner is back (other than off-days for Bohm and sitting Turner against LHP). It's all well and good to say they want to keep Sosa's bat in line-up but he's not going to play LF more than once or twice a week if that, and will likely not stay this hot once he can't play every day (or even if he could).
It will be interesting to see if Dahl forces their hand. Once Marsh comes back, after Turner (who will replace Wilson), either he or Pache has to be DFA'ed (or Merrifield does) and Clemens won't be back (has options). Only other path would be demoting Rojas.
If they are serious about it all of it, they'll make a reasonably significant trade deadline acquisition and that will domino everything, including changing Nick's role a little. But that's not likely to happen in the next four weeks.