@qwerty 613 about one in 300k – you already asked this question, and i already answered it, see other thread there are gemaros, medrashim, zohar, kisvai ari zal etc that say different than that gemara. (like many machlokesim in gemara)
see igros kodesh vol 1 letter #85. one source brought there example ועיין בסנה’ (קד, ב) דורשי רשומות היו אומרים כולן (אפילו ירבעם וחבריו) באים לעוה”ב
the rambam clearly writes in igeres techiyas hamasim that moshiach can be from the dead.
if you say moshiach can not be from the dead, you will need to find at least one makor in chazal, then you will have a machlokes!
if you look into the sugya you will be there are 2 ways for moshiach to come, if we merit or not, if we merit there will be miricles from the start, if not the miricles will only happen later, so the rambam in hilchos melachim is explaing al pi halacha the natrual way for moshiach to come, thats why the chasam sofer and others write that in every genaration there is someone fit to be moshiach who is alive, so that natrually moshiach can come every day. but moshiach can still come from the dead like the rambam writes in igeres techiyas hamasim. and like the gemara says. look in the safer dvar malchus, over 600 pages explaining hilchos melech hamoshiach in rambam.
look at wikipedia and the footnotes about reb shach, moshiach, chabad when he went against chabad