I don't think Dan dies. In the preview of Day of Doom, it is revealed that Amy poured the serum out in the drain and replaced it with some sort of icky vegetable mix, before Dan had a chance to drink it. Also i would be shocked if one of the main characters died. I think that maybe 2 more of the hostages might die, probably Natalie because there was a code on the cover which translates to Natalie and maybe someone in the Vespy council. Or some minor characters.