These are not nafka Minas at all.
1) The expression shlita (what it stands for) only really makes sense for someone alive in a physical body. But it’s not really factually that wrong since the nefesh hachaim says clearly באמת* אינו מת* and עדיין* בחיים*. Direct quotes. Again I’m not advising it but if you have אמונה that what the nefesh hachaim is saying is actually true it’s not factually wrong that a צדיק is alive (without a physical body) just not an appropriate expression.
2) moshiach has nothing to do with it at all. Just because someone is alive doesn’t mean they are or can be moshiach. And just because someone is dead doesn’t mean they can’t be moshiach. The Rambam writes that techyas hameisim is one of the 13 ikkrim, so we all have to believe in it. The same Rambam writes in iggeres techiyas hameisim (which everyone agrees was written by the Rambam himself) that techiyas hameisim can happen either after or before moshiach. Now if techiyas hameisim happens before moshiach there is no source or svara to say that just because someone experienced techiyas hameisim that excludes them from being moshiach. So one of those who went through techiyas Maisim could be moshiach. Again being alive or dead or moshiach have nothing to do with each other.