Anyusername: “In your words you can say the abarbanel is arguing with rashi”
You’ve gotten it wrong again. The Abarbanel is quoting a Yerushalmi whose veracity, he points out, is seen as problematic by a number of meforshim. So he explains how that Yerushalmi need not be problematic.
One of the points he mentions is that according to the Yerushalmi this “moshiach” would have to return from the dead. So he writes that that is not a problem as in Sanhedrin there is also a way of learning (as Rashi says) that moshiach is Doniel who has died.
Nowhere that I saw even hint that one can say that a different dead person is moshiach – not according to the Bavli or according to the Yerushalmi.
One major point: even were there to be a clear source saying that one can choose someone who is dead and believe that he is moshiach, that wouldn’t stop us saying that your rebbe CAN’T be moshiach. There were too many problems with him, not the least of which is the atzmus sicha. We said this when he was alive and ALL of lubavich were claiming that moshiach HAD TO be someone alive.