It didn't delete my iTunes library, thankfully.
When my iPhone was bricked, this is what happened.
1. I connected it to my Mac as it was just plugged into the wall prior
2. It wouldn't download the update for a while, but would pretend to I guess. I would click download and wait about 5 minutes before it game me this error
3. I then noticed that it was trying to download 9.3.5, so I updated iTunes to the newest version.
4. I tried doing this again and was met with the same error 1671.
5. I also got this error but Apple Support told me to not worry about it.
6. I thought maybe my Mac not being charging would have an affect on this, so I plugged my Mac in and then tried to update once more.
7. It finally started to update, with my iTunes saying stuff like "Updating iPhone Software" and "Verifying Updated iPhone Software". My iPhone switched from the plug into iTunes screen to just the Apple logo and the progress bar.
8. From there, everything went smoothly.