Q1, what does it mean, how is it different from being dead?
Check the meforshim (Rif, Iyun Yaakov, Etz Yosef, Ohr Hachayim) who explain it at length. You probably still won’t fully understand because it’s something completely supernatural beyond out understand. Ask Eliyahu Hanovi to explain it when Moshiach comes.
Q2, who is authority enough to say that if Yaakov aveinu can get to lo meis status then we can say the same about the LR?
No one said that in this thread. Completely unrelated to this discussion about Yaakov Avinu.