philosophically speaking: what now? the entire goal of humanity is a complete understanding of particle physics? :p
if your questioning the future of the scientific community beyond that, that is a much more interesting matter IMO. i think if that happens, the social drive for better understandings behind science isn't going to go anywhere, and if we have one theory that explains everything, younger scientists will come up with parallels, and with no new predictions to make, it will come down to bickering over natural philosophy, logic, various versions of Occum's razor and the questioning of it completely, and with no proof to go by, will most likely end up competing on various social and psychological appeals, possibly ones that touch us on such deep emotional levels, seem so obvious once understood, that we might find it hard to not become appalled and even offended by mentalities that rejects the ones that speaks most dearly to us.