It depends ! If it is Kirch, and they are insolvent - i'm not sure if they can sell on the rights to a new owner or whether they would revert back to Henson if the company went bust. In whatever case, until those rights come back under Henson control then any new parent company would have to wait until they did to do anything with them. So, in a nutshell, probably 2050 - but theres nothing to stop Disney, Time Warner, Viacom etc trying to buy themselves out of the deal !
This is basically the thing - the new owners will still have to take on all of the existing Henson deals be they merchandising or output (so Palisades, Sideshow, Columbia, Fox etc etc) but if they desperately don't want to continue and want to use their own people straight away then they could buy themselves out immediately (at serious cost) but in most cases new parent companies just go along with it until they can safely get out of the deal without paying up, then do their own thing.