ending??

So Darkseid's plan was to come to earth, beat up Superman (and Supergirl if she got in the way) and then just leave?

Did he think he had killed Superman, is that why he was going to leave? Did he spare Kara because he was still considering using her down the road, seemed out of character for him.

And what exactly did Superman gain by preventing him from leaving and then continuing the fight for a few more minutes before then forcing him to leave?