Trump was pretty clearly upset with Kelly to the point he was rage tweeting, but in the end he needs Fox News more than Fox News needs him. Trump is still getting almost glowing nightly coverage from Greta and Hannity and that is better than he is going to get anywhere else.
The campaign is just beginning and though polling very well for the moment, to alienate Fox News (the only major network even remotely fair to Republicans/conservatives) would be idiotic. Trump is smart enough to know better.
This spat makes both sides happy. Trump can hate on Fox News for a bit which might please some voters who detest Fox News and make Trump look more independent, and Fox News gets to look more divorced from the GOP and therefore more "balanced". And of course all this sets up the inevitable Trump interview on Megyn Kelly's show. And that will happen at some point.
Couldn't agree more.