Depends on the service. For example, if proton bans me I can move my email to a different provider because I own my domain. In case of Obsidian, it's an offline app that uses Markdown, so I can easily migrate to a different note-taking software for any reason.

Your backup note is on point; I highly recommend everyone to do a Google Takeout every few months (or at least years!!). If you've never done one, like most Google users, you're playing with fire.