I have to admit I don't really like seeing a mature and respected project such as Vim being forked with its fork getting momentum, but let's not forget the fork didn't happen yesterday - Neovim is more than 6 years old already. The main reasons it is getting momentum are its built-in Language Server Protocol support, and Lua integration instead of Vim's scripting. Both are undeniable upgrades. There are other reasons too, which I consider minor. There might be other, less technical reasons as well, but people just speculate about those and I wouldn't bother.
I understand some people are used to Vim for decades, so they dislike the replacement of Vim with Neovim. I use Emacs myself, and I wouldn't like it if it was replaced with, say, DoomEmacs, so I can perfectly understand your concerns. What I would do if this happened would be testing the replacement first; if I didn't like it, I would install the original Emacs right away and forget about its replacement. I recommend you do the same with Vim; you still have the option to never use Neovim, if you so wish.
I wouldn't be worried about the future of Vim either. I migrated from Vim to Emacs years ago, and over the years I have seen many Emacs forks promising this and that - guess what, the Emacs community is still there.
Last but not least, we are not talking about a huge change. It is not like systemd, which is blatantly not what it was supposed to be. Neovim is still Vim, even though the two projects increasingly deviate from each other.