AFAICT, no one has been so stupid as to do that in the past (renege on a promise to honor lifetime status from someone they merged with). I believe that even when American acquired SOME of the assets of TWA from bankruptcy, they honored all the programs.
-Rick, proud owner of a Lifetime Delta Sky Club Membership (This is something you could never buy directly; Delta went so far as to honor lifetime commitments to Northwest flyers even when they didn't have an equivalent program.)
AA only honored my lifetime TWA lounge membership for about a year. I haven't flown AA during my lifetime since then.
BTW, I just made LTP (0 stays and 0 years as Plat to go according to the semicircular graphic on my dashboard), but it still shows me as Plat and Lifetime Gold earlier on the dashboard and also on my account summary on SPG.com. How soon does it currently take to (1) have the status show on my account, (2) get the plastic card showing LTP in the upper right corner, and (3) get the nice boxed kit with the metal card? Thanks.