CS, where does rav moshe say anything of the sort?
Complete fabrication. No one said that until messianic Lubavitch.
Yaakov lo meis means Yaakov didn’t die. It doesn’t mean that anyone else didn’t. Eliyahu also didn’t die, and neither did chanoch.
So what? The Lubavitcher Rebbe died. He had strokes and physical health problems just like anyone else. He’s no longer living. He’s not yaakov, eliyahu, or chanoch.