What is Mikage's status (in the spirit/god world) after he passes the Tochigami Crest to Nanami? Is he still a god?
It's not as present in the anime as in the manga, but Mikage takes the shape of a butterfly and you can see him fly around in the manga at all the important events and otherwise. He's constantly monitoring Nanami.

I believe he is still a kami deity, just not the deity in charge any more. I've interpreted it as the crest being a sign of her taking on the godly responsibilities and in all practical manners is a god, even though she is still human. He's still the shrine's god, he's just handed over the practical responsibilities to Nanami.

Your race doesn't change just because you gave away or received a profession.

This is my interpretation at least.