They've shown no real indication of doing that. Castellanos has worked out there a bit but said it would only happen in an emergency. Is Hall getting hurt an emergency? Maybe. Is Harper even going to return to the OF this year? Also maybe (but I think doubtful, not to mention he might not be good defensively given the rust and age, when he was already declining).
With or without Harper they are team that's light on offense. If Schwarber or Castellanos plays first somebody still has to DH or play an OF spot. Bohm at 1B and then living with Sosa at 3B (with the possibility of him having great upside) still seems like the play. If it's not, getting a RH 1B bat to pair with Hall is, and why wait? Putting Schwarber or Castellanos at 1B just means you have an even worse 1B situation than you did with Hoskins. And right now just putting them at DH means playing Jake Cave every day, who's nothing special defensively and has a career. 297 OBP (which is still better than Hall's a realize, but much larger sample).
Certainly they could afford to let things play out with the internal options and mix-and-matching, but that was before both Hoskins and Hall got hurt. And unless they are already conceding the division - which may be fair enough! - a month of not doing anything about it when there are also pitching issues may prove costly.