AA awards lifetime platinum (for the lifetime of the platinum program, incidentally) for travelers who accumulate 2,000,000 miles from all sources in AAdvantage. This will be retained through the acquisition.
TWA miles that exist as current balances in TWA accounts will be merged with AAdvantage accounts. Whether the AA total mileage counter is "on" or "off" for the transfer is unknown. If on, balances greater than 1MM will generate lifetime Gold on AA and balances greater than 2MM will generate lifetime Platinum. No lifetime status at the Executive Platinum level exists (and that will probably continue to be the case going forward).
I suppose the question is: how many TWA frequent flyers have account balances currently in excess of 1MM and of 2MM. If not many, AA will probably turn the counter "on." If there are thousands, they may decide to leave the counter "off."
More directly to your post: I doubt that AA will honor TWA lifetime status once TWA flights discontinue. Probably one or two years of equivalent status, like the clubs.