I definately think it'll be a supervirus; due to the population constraints that we are putting on the globe and the modern 'vectors' make this a possibility. Additionally, global warming resulting in elevated water could cause mass migration and major problems which could facilitate a superviral outbreak...Basically, we are all gonna be fodder for some bug and believe me we (re: general population) will get wiped out. However, I do think that we as humans will persist it is just that the core (90%+) of the population will collapse and given the modern industrialization of supplies (think about how many people/resources it takes to get fresh water to our houses) most will die within the first year, but I think some will make it and re-populate the planet (albiet slowly).
<my 2 cents>