RUU Flashing Doesn't Work... Help! topic

Okay, this is a pretty interesting situation. I rooted my dad's gunmetal m8 and everything was fine until the OTA update came out. Despite me telling him not to download it, he does anyway and the phone tries to apply the update. He then had a persisted "there is an update available" notification, so he decided to take it to the Sprint store instead of calling me... now it's too late.

I have no idea what they did at the store, but now the phone just reboots every 3 minutes or so. I've tried restoring the NANDROID backup, reflashing new roms, flashing the stock recovery, flashing new versions of TWRP, but nothing, I mean nothing works. Every time I try to do anything to the phone, as soon as I reboot it, the phone is IN THE SAME STATE IT WAS BEFORE THE OEM UPDATE. It's like a weird version of groundhogs day.

Best I can tell is that the bootloader got corrupted and it keeps flashing the same copy of the old rom again and again and again on reboot, so I can do absolutely nothing with this. Whenever I try to flash a new ruu, I try fastboot oem rebootRUU, but when I do, the phone just reboots and repeats the cycle.

Is there any thing I can do, or is this thing a paperweight?

Thanks in advance.