Gilchrist has already suggested that he might be retiring from ODIs, hasn't he? That would be a perfectly reasonable move, maybe at the end of this summer, depending on how he goes, and how motivated he is in the format.
I don't see any justification at all for dropping him from the test side, though. He didn't have a great Ashes series, but it wasn't exactly abysmal either, and his keeping is fine. Every player has bad patches or periods where people question them, witness Hayden leading into the CB series last summer, Ponting in 2004, McGrath about every 2 weeks for the last 5 years of his career etc. Once a player reaches a certain age every patch of poor form suddenly puts them on the chopping block, at least in the eyes of certain kinds of fans, but it's certainly not justified yet for Gilchrist IMO. Even if he is permanantly past his best, he is still a fine keeper and, after all, a number 7. If he only averages 40 it's hardly going to drag the team down.