The Rambam is rather clear. Once someone dies, they are no longer eligible. Claiming the Rambam meant only killed not dies is kind of laughable, especially since the Chasam Sofer says quite clearly Rambam meant either or. Claiming the Rebbe didn’t die is also laughable. We all saw footage of the funeral. Plus I know one of the people who transported the body from the hospital. Tight chain of custody. No yechi chanting will change that.
There’s a list of self-declared Moshiach candidates throughout the years- Yoshke, Shabsai Tzvi, Jacob Frank, R’ MM Shneerson, et al. Each time people say “this one is different”, he isn’t.