Regarding the supposed “contradiction” from Sanhedrin 111a. –
The hekesh is from the Redemption of Mitzrayim- when all those Yidden (other than the 2 out of 600,000) died, and specifically during the plague of Darkness so that no one would have to witness this.
IOW, it is not that ch”v any Yidden were denied the ability to leave Egypt during the actual redemption, and had to stay back…all the Yidden who were alive at that time indeed left (and there is even a [midrash?] telling of how dasan and aviram stayed back for the parting of the sea, and Hashem split it open once again JUST for these two (reshayim though they were). – it’s a separate question how it is that they left Egypt, if indeed they were the reshayim that we know them to have been…
So too, as per the hekesh, we can conclude that all those Yidden who are not part of the 2/600,000 who will be alive for the redemption, will indeed be redeemed, whereas the rest will have to die some other way, presumably in a fashion unnoticed by the general public (as per the original redemption from Egypt)