You won't lose any data upgrading to the stable version when it is out.
The only real question is whether any third party (non-Flarum) extensions you use will update to that version. But our community is pretty good at updating most of them, so I wouldn't worry too much about that part.
As for re-installing, Flarum actually makes it pretty easy to do so, all you'd need to back up is the following: database, assets folder, config.php, composer.json and composer.lock. Everything else can be rebuilt quickly and painlessly, so even if this is required for stable (which I don't expect), it won't be an obstacle.
