Thats kind of an insane thought to have lol.
Eh, I always thought it kinda made sense. Luffy's not one of those no-kill Nancys after all, unlike a certain Gothamite from DC.
I don't think he could have damaged him seriously enough in time either, unless he ,say, enlarged his fist to Bajrang Gun size extremely fast while still holding Kizaru and then squeezed really hard.
Which, considering that Kizaru has eye lasers and a lightsaber that he could use, would probably be hard to do without the Admiral freeing himself before it happened.