TSA has not issued any requirement to be removed if you are on a LOA, be it MIL, Voluntary, medical, etc. You MUST be removed from CASS is you are subsequently furloughed.

CASS is for cockpit access only. UA, DAL, CAL, SWA....none of them requires your CASS data to be positively verified. There are some agents that don't know better, but the airline policy does not require CASS for a cabin seat. Some airlines want to process you through CASS when you check in in case you end up in the cockpit (CAL, SWA DAL, and a few others), but if your CASS query comes back denied you will be restricted to a cabin seat only (exception is Alaska, Horizon, and maybe AA).