Regarding Yaakov Avinu Lo Meis, it doesn’t mean that he didn’t pass away. It says Vayigva, which means according to one meforesh (on Avraham Avinu’s death, as I recall) that he became ill with choli meiayim before he died and then died.
The gemara in Taanis questions on the spot that they embalmed Yaakov and were maspid him, etc. so how could you say that he didn’t die? The gemara then answers that it does NOT say vaYamas because there is a drasha to be made from that omission. But, of course, he did pass away. He is buried in Mesaras haMachpeila. He, himself, told Yosef that he will die “meis”. Etc.
The Zera Shimshon (on ViZos HaBracha, if memory serves) quotes the Zohar that Moshe Rabbeinu lo meis. He says that “meis” means, if I understood correctly, that the neshama ascended to a higher state upon dying, meaning higher than that in which it was previously when alive/in the body.
So, he says, that both by Yaakov and Moshe, their neshama was just as pure, etc. while alive in their body as afterwards when they died and the neshama left their body; Yaakov Avinu, due to all the yissurim that he had in addition to his holiness and purity and Moshe Rabbeinu, of course, being the navi that only he was, etc.