“what other moshiachs?”
Chat,
In every generation there has been someone who would have been Moshiach if we were worthy. If Moshiach can’t die, where is King Chizkiyahu, who was designated for his generation? Also, where does it specifically say that Hashem took an oath that Moshiach can’t die?
You should be able to answer these very simple questions simply, without very lengthy circular logic and hyperbole.