As far as I know, skin rotation decisions are all up to HTC, but I would expect all of Fester's skins to be a lock to stay in game. They are richly detailed and beautifully made. Great for studying the use of glare/shadow layers to create the look of an uneven surface.
I would also expect any skin seeing regular squad use to stay in game, unless maybe the squad CO would ask HTC to have their skin rotated out and replaced by a newer, more detailed skin intended for the squad. My impression is that HTC is committed to squads and wants to take good care of them.