Why would you lose your phone? If you're worried about your data, back up everything with the MIUI Backup app, or if you're planning on trying other ROMs, back up your apps with Titanium Backup. Then you can do complete data wipes and then restore everything when needed.
Nothing I told you to do will hurt your phone or data if you use a backup app. It's completely normal troubleshooting to see at which point the problem occurs. If you do a compete wipe (data, cache, Dalvik cache, and if you're using Amon RA, it's a good idea to wipe boot and system also), you should be starting from a completely working state. That way, if an app is causing the problem, you'll know because tethering will work until the app is installed.
Before you go through all that trouble, though, check to see if your tethering works while the app is uninstalled. Then, you won't have to worry about your data.