Nick said he was going to bring his 1B glove when Hall first got hurt, but it was never seriously discussed. And Schwarbs remains a non-option I think.
So let's just assume Harper is the 1B and Rhys isn't coming back. It's been pretty strongly implied that Rojas won't come into Clearwater as the starting CF, which means Marsh is. Who do you sign for LF (with Pache as Marsh's back-up/the extra defensive OF)? The top FAs after Bellinger (who, let's be honest, would actually be perfect - he's the antidote to all the other defensive flaws because he can play all three OF spots as well as 1B) per MLBTR (with their projections) are:
Teoscar Hernandez (4/80M)
Lourdes Gurriel Jr. (4/54M)
Jung Hoon Lee (5/50M)
Jorge Soler (3/45)
(essentially a DH as is JD Martinez and of course Rhys. Plus Mitch Garver, don't know if he can play other positions besides catcher)
Harrison Bader (2/20)
Whit Merrifield (2/18)
(can he play LF?)
Jason Heyward (2/16)
Brandon Belt (1/15)
Hoon Lee is 25 years old and an OBP machine so I'd certainly be interested. Bader and Merrifield maybe. Heyward is the essence of a part-time LH bat who still fields well but do they prefer a RH? Belt could be your 1B (big LHB, takes walks).
But they are more likely to be shopping for a part-time/one-year player especially if Marsh end up in LF by June.
It's true that they don't need to "replace" Rhys but they also missed Rhys. The question is how can they get better, and at what positions? Running it back may or may not be fine until the deadline but we also can't assume all the returning players are better next year (young or old).