I've used these as well - you can get a box of replacement screws on amazon for ~$18 after you buy the initial package in case you need more.
I've had to remove some from the floor and it is a bit of a pain. You have to chip or drill out an area around the broken screw, then grip with a pliers to twist them out. It's not a huge deal though as it shouldn't really happen often. If you are replacing the whole subfloor you'd likely just saw out the entire area then either chip away the wood by the screw or just tear it out of the joist with a crowbar. Really, you shouldn't be replacing the subfloor unless it's been compromised by water damage, ants, etc