Install custom rom for specific device via recovery mode, power button + volume up.
Gingerblaze is specific rom for Alcatel 918 MIX (google this not sure if i'm allowed to post external links)
Use Alcatel's one touch upgrade software to download stock rom.
This method gets you out of recovery mode booting loops(i was stuck in this one), gets rid of unwanted roots (for when bring in device for servicing to ensure that your warranty is not voided). I was also rooted using blue rains' method for the Alcatel 918N, it works well with the MIX no issues btw.
Hope this helps!!!!