And yet somehow Cave put up 0.6 WAR in 164 ABs last year (not literally replacement level) vs. Hall's 0.4 in 136 ABs. The key decision point, if it really does ever come to one, would be that someone like Cave makes the team better with a little defense plus, more importantly, by putting Castellanos at DH. Whereas Hall makes the team better with a little offense but worse by putting Castellanos in RF.
The better solution, obviously, would be to find a player who has some of both attributes (i.e, better hitter, can actually play OF). And you could also make the case that Maton might hold down RF part-time just as well.
Granted the pitching churn could make roster space tighter but my guess is the Phillies would be happy to keep Cave on the 40 and in AAA. If Hall breaks camp as the DH and Vierling keeps his job they still can use a LHB OF who can play all three spots on call, unless they are ready to use Muzziotti. If they had to make space for him tomorrow they could just ditch Ortiz.
Or perhaps Cave's "replacement" will be here in just a few days (i.e. via Rule 5. Then by the time Harper comes back maybe the old team lets you keep the player, or you don't care anymore).