"Keep Your Drive" is now a non-free (but not that expensive) "service upgrade". Disks are still removable on most models and it's not hard, but you still have to open the bottom of the laptop. (For ThinkPads, through ultra thin models like the X1 or "unusual" models like the ThinkPad Yoga might be more problematic.)
EDIT: Through it also depends on you service/guarantee contract. If you normally have a service contract where a technician will come to you but for some reasons that currently don't work you probably can keep your drive anyway etc. Also KYD extends to some other cases.