Quote Originally Posted by Khiraji View Post
DO NOT attempt to SBF once this update has been applied - will brick your phone. I foolishly tried that on Monday, and have been without a phone ever since.

There is an app on the market called RootKeeper which, if downloaded and installed before the update is applied, can apparently preserve root. Definitely look into it.
I suggest that D2 users contact the OP of that thread, [How-to]unbricking downgraded 629 & root normal function OTA 629 - Droid 2 / R2D2 / Milestone 2 / Droid 2 Global - RootzWiki
to see if he has plans to do the same for the D2. This looks like a general trick