what would nihilus do? he would already have drained or stunned luke before he did anything. if luke removes himself from the force, nihilus would stun him then cut him with a lightsaber.
for luke to kill nihilus he would have to use green lightning as his first move, and if he does that there would be a delay and that is when he lifts his hand up while nihilus force drain can be done standing still and doing nothing.
ok the thing is the last thing luke is going to want to do is to remove himself from the force or alter the gravity because doing that would give nihilus the upperhand of winning the fight.
lukes best chance is green lightning and not anything else, nihilus cant be cut from the force because he is already a wound.
"Aside of this Luke can create "loops" in the force at will. Technically he can create some force field that keeps feeding Nihilus meaning the drain would again not effect him."
-from borbarad
how is he gonna do that if nihilus uses the force drain as his first attack? he is stunned, no matter how powerful luke is he cant move or do anything. nihilus did that to an entire planet full of jedis
and even tho luke is at a higher level he still effects him,
even a simple stun effects luke allowing nihilus to attack with a saber and even if the stun is only a split second, luke will already be finished.
so as i say lukes best and only chance is to zap him with green lightning where nihilus completely has no defense against.
the force drain may not seem like an instant kill but it is, remember kreia doing it on the 3 jedi masters? she did it at a lower level and once it hit them which is incredibly fast, they are already dead but the force still getting sucked out from them