While BFS is pretty stable, your physical hard disk is still subject to heat, wear, and tear. It’s possible for bad blocks to occur, and if they occur in the wrong place, you could be up the creek. If your system stops booting, try the techniques listed in Distaster Recovery. You should be able to run DriveSetup on your hard drive even if it won’t mount your partition.
Run the Surface Scan from DriveSetup to check for block integrity. Even if the test makes it all the way through without finding errors, it will move any data found in bad blocks to new blocks, which could mean that you regain the ability to boot normally. Almost like having a little built-in Norton Utilities. Certainly worth a try before reinitializing your drive.