I had the same problem, because I tried FDB theme on PR1.2 beta on N950 while the theme was designed for PR.1.1 (it was the latest version publicly available for N9 back then).

If you have SSH and developer mode configured you should be able to fix it without reflash. WiFi was not starting for me but I booted Linux on my laptop and connected the USB cable, selected SDK Mode and the I was able to login to N950 through SSH (ssh user@192.168.2.6 - iirc).

Fixing it is a matter of restoring the original theme files, you can find them on FDB theme thread, 1st post.