Wallpaper etc could be that some of your settings were wiped, or that it was factory reset. Apps being missing could mean it has booted into safe mode (which a broken button could cause), but that wouldn't account for the account itself going missing (if that means what it sounds, i.e. you had to enter your Google account login again). But what do you mean by "software"? Nothing can revert it to an earlier OS version.
The user account being deleted points to it having been reset, though obviously I can't be certain just on the basis of the few words of information here. And of course you have said that it "broke" and "died", but not what exactly happened there.
There's nothing to stop you entering your new account login into another phone, and stuff that is backed up (e.g. any contacts and data that are synced with the cloud) will be restored. But data that have no backup are unlikely to be recoverable if they have actually been deleted.
