I don't know how that would affect root, or Magisk hide, as I know a lot of that has been nuked since topjohnwu got hired at Google.
I also currently have Magisk hiding itself, which may make even an uninstall difficult if I even knew what to install over the top of it.
Uninstalling the Magisk Manager app would not affect root; you might not be able to run certain rooted apps properly without granting them root access, but that's because of not having the Magisk app to grant it.
I don't know about topjohnwu being hired and working for Google or what not, but Magisk is still being currently worked on and developed so it has not been "nuked"...
How is Magisk Manager hidden
"itself" if you claim you attempt to run the app and it force-closes? The only way for Magisk Manager to "hide
itself" is that it merely renames itself (to a name you can choose; default is "Settings") so it's not detected by any root detection. In any case, you should be able to find it in the Apps list in Settings/Apps, and uninstall it that way.
As to what to install over the top of it, installing the latest stable 25.2 would be the best idea -- the Magisk App does not need to match the version that is patched and flashed to your boot partition...