How do I delete a BootCamp partition using Terminal's diskutil?
Here's what worked for me:


use diskutil list to find the small Microsoft Reserved partition you're trying to delete but disk utility (or the command-line equivalent diskutil) won't allow.  Let's say it's on disk 99 partition 400 (mine was on disk 0 partition 4)
sudo diskutil eraseVolume JHFS+ deleteme /dev/disk99s400


The above reformats the partition to journaled HFS+ and once you've done that you can just simply delete it (and then resize etc. as you wish).

Note:  I've used /dev/disk99s400 because that should not ever work, you have to replace those with the right disk and partition.

WARNING: Destructive, high risk. ALWAYS do a full back up first before screwing with partitions.  ALWAYS.