If Koyo-koyo (huehue) is on the verge of becoming a vampire the second time, doesn't the servant-master rule apply? I mean draining Kiss-Shot again so he can return to being a 1% vampire like before? Or is he becoming a "free" vampire, thus being unable to restore his humanity?
Now if that's the case, then he's getting a serious bite in the ass from luck, and now he has to choose: abandon Shinobu, retain his already dented humanity, BUT let her die OR maybe sacrifice himself once again so they both live. But that would be seriously out of character, because he would now have to hunt for humans, which he didn't want in the first place. He would also endanger everyone in his little harem (albeit a bit thinned out), and most importantly: Hitagi.
He would be immortal, thus he would live X time longer than her, which would basically mean the end of his relation with said recovered tsundere.
Not to mention that vampire hunters would swarm in his direction if people started to disappear...
So all in all SOMEONE has to die: Koyomi, Hitagi or Shinobu.
Fourth option? Knowing Nisio: NOPE
Although, i'm kinda hoping for some kinda deus ex machina here, because the fans would prolly go ballistic after a bad ending
I know that in Hanamonogatari it's written that Koyo and Hitagi live together blabla college bla, but we don't know the details, do we?