It's not going away any time soon, the app is still available for MacOS and the browser extensions work just fine. Eventually they will stop supporting them but that'll just mean at some point in the future a MacOS/firefox/chrome update will break the existing app and they won't fix it. That might be 2 months from now or it might be 2+ years.
And once that happens, you may no longer be able to access your passwords.
Sure, if you longer have a way to use an older version of MacOS. Not a good idea to leave your sole copy on a machine you don't have full control over.