If he has the plot and ending already planned out, I doubt online speculation would affect him much.
On the other hand, it wouldn't be out of the question for him to have workers keeping an eye out for fan reactions, especially regarding pairings. It's happened before (in other forms of media) where a love interest for a certain character was introduced and then later discarded / the pairing was killed off because of bad fan reaction.
But this is a manga and Kishi likes teasing, so if he chooses pairings in the end it probably won't matter to him since the show would have run its course. I think leaving it all up in the air would piss more people off than if he just decided things, though, so there probably will be some kind of resolution...