no, infact you never NEED to extend legally. you might choose to extend to get a slot or position or to attempt selection or even to clear so you can get all of your last paycheck, but you cant be legally forced to extend.
in your situation, no you wont. the military did away with involuntary stop loss. you can CHOOSE to extend for some extra pay, or they'll send you home when its time to ETS or just keep you on rear-d.