As we know, there was an extension named "LiquidThreads", that has almost the same functions like Flow. Unfortunately, it is unmaintained now, and the discussions there is not exist now.
I want to ask that will Flow be stable? Can I backup the discussions of Flow on my MediaWiki website if it has some issues?
@Rubyy, we are migrating all of the LiquidThreads discussions (including history) to Flow on MediaWiki.org (this is all done except Project:Support desk, which is in progress). Certain other Wikimedia wikis will come later.
If WMF ever switched away from Flow to a new discussion system (there are no plans to do so), I would hope we would migrate Flow content to it, similar to what we're doing with LQT->Flow.
We will work more soon on public database dumps for Flow (phab:T89398). However, just as with regular pages, this will not include 100%. E.g. the main public dump can't include deleted posts for obvious reasons.
So dumps are a way of providing your content, but they are not a complete backup. Thus, even if you choose to provide dumps on your third-party wiki, we encourage you to also back it up at the database layer (e.g. tools like mysqldump).
Also, this LQT->Flow conversion software is in the Flow repository for anyone to use if they choose.
I wondered the same for a while but I'm ready to give it a go.
I now wonder if it's stable enough so updates won't make big problems. I guess not since it's enabled in some Wikimedia projects.