You make the Caps seem a little bit like cupcakes. If losing him now can crater their morale for this run, then losing him in the summer can crater their morale for the next run. What about the boost of morale from adding a big piece (which would be the only reason to trade Holtby in the first place)?
Subjectively, the only Caps whose departure would make me somewhat concerned in terms of team morale would probably be Ovi, Oshie, Wilson, maybe Backstrom.
Anyway, for me the significant argument against trading Holtby is the simple one -- he's all but played his way out of DC, but he still has Cup experience, so trading him to be left with Samsonov/??? for the run better be really worth it in terms of making room for a major piece... which, while possible, seems unlikely.