It won't die. Its not a problem to skip auth checking if at some point MS tries to use kill switch (hopefully EU would make that fully legal in EU if that's not provided by the company).
As for feature parity, there are mods backporting modern features back to 1.7.10.
Java is also portable to all the consoles, its just Microsoft did use that as an argument to try to kill the Java Edition. Nobody prevented Microsoft from adding bedrock like modding to Java Edition.
The only thing that needs to happen is the one single stable mod API for Minecraft Java Edition. The incompatibility between Forge, NeoForge, Fabric, etc. is terrible, but from what I know about some of the folks involved this won't happen as they cannot constructively discuss the matters.
Nit/Correction; Tamriel Rebuilt is not about adding all the Tamriel but only Morrowind mainland. What you might be thinking about is Project Tamriel [0] which tries to add Cyrodill, Skyrim, High Rock and Hammerfell. They're working in collaboration with Tamriel Rebuilt so they are all compatible and share many resources.