Jothar, you are wrong. On the contrary, R’ Aharon Feldman’s position is that to say the Rebbe is alive is not apikorsus, even though he believes it to be a lie and a foolishness, as long as one is not asserting his divinity.
This is his letter: http://moshiachtalk.tripod.com/feldman.pdf
(Mods, please let it through – it is just this letter)