They'll keep an extra catcher or two around in extended that is a bit older just in case they have injuries.
As for the top of the system the biggest question is whether they move one of their top 3 catchers. If they trade one AAA will have Moore and this new catcher or another catcher yet to be acquired with ML experience.
If they do not trade a catcher they send Rupp or Knapp down (most likely Knapp) to play every day with Moore backing them up.
I lean towards the "trade Rupp" option. I think the new regime likes Knapp because of the high OBP and switch hitting. So they probably make sure they have a veteran in reserve at AAA.
BTW three catchers on the ML roster has near zero possibility. Besides the talk of a short 4-man bench, there is also no longer the need to have one of the catchers occasionally play 1B with Santana and Hoskins. One can only have 2 catchers on the ML roster in that situation.