Default [Q] Restoring encrypted rooted to stock

Dear all,

Have a bit of a problem. Have a HTCOne Dev Ed. Android 4.4. Had to encrypt to allow work exchange mail to work. Has also been rooted and has TWRP recovery.

Now have a problem. Because of encryption, cannot mount the drive in TWRP. Also means cannot get OTA updates to work. Cannot do a factory reset either.

As I see it, only way to remove encryption and restore to factory stock would be to S-off and run a RUU of the stock. Does anyone have any other suggestions? Also, would rumrunner run into any problems due to the encryption. Don;t really want to brick a functioning phone.