If we ever "lose user account data" and ask you to sign up again (or remove account functionality entirely), then you should not trust this site any longer.
If this were to happen (extremely unlikely), then this site would now be an FBI honeypot.
You would also likely start to see "mods" (not us) encouraging all to post violence.
I believe you can trust this site for as long as your user accounts work, which will hopefully be forever.
Keep in mind that to verify whether your user accounts do work, you also need to check whether an incorrect password doesn't work.
To follow up on my last point -
If we assumed that our lovely forum was stolen (everything except our user database), then one option would be to set the password to the password provided in the first login attempt, regardless of what it is.
For example, if nobody has logged in as u/Doggos before on our honeypot site, if I try to login with my real password ("Hunter02") then the honeypot site could set my password to "Hunter02".
In most situations, the first login attempt will be from the rightful owner with the correct password, so many people would never notice that the site had no idea of their password until they provided it.
That's why, if you've been suspiciously logged out, try to login with an incorrect password first. If it works, then that's bad news.