The quest started fine, got to the top, then when I talked to him and selected the "Let's do this" option, he responded as if I had selected the 'wait' option. I shot the nightkin up ahead before I talked to him, don't know if that matters or not.

Okay, while I never got Neil to help me do so, I killed Tabitha and finished the quest. He went ahead and gave the ending dialog. Also, I just thought that he might have been bugging out because I already had a companion, and so he couldn't go with me, but idk.