Just asking have you talked to someone in your fleet? Perhaps you can simply get reinvited. Cryptic has a habit of losing information like your equipment, doffs, ect... but never heard of them forcing someone out of a fleet. Not saying it isn't possible....
Second idea a Undine has replaced you and you are targeted for termination.
Im from the same fleet and have the same problem,
but we cant get a reinvite as the fleet is no longer on the fleet lists.
Also the only ppl ( there was only 3 above our rank)who could have kicked both of us have not been online yet and are in the same FED fleet as us.
What do you mean by "gone"? Just because a fleet does not appear on search does not mean it no longer exists. Just that it is hidden from the prying eyes of randoms. Have you talked to any of the people who are supposed to be there?