Conflict Ideas for a Novel?

I'm writing a novel that is pretty set with characters and their conflicts. The story revolves around several individuals who are killed but within a few days are brought back to life and realize that they are immortal and cannot die and that they have their characteristics accentuated including strength and speed etc. The characters range in occupation from a drug addict to a Mormon missionary and each has there own internal struggles they come to terms with and grow from their immortality... but the big issue I have now is what is the big issue they have to come together to deal with? Why should they stick together and what is the overwhelming larger force they need to overcome with together? It seems the only big issue I can come up with is a corrupt government or war or the evil super power threatening world destruction or domination... which has been beaten into the ground in so many books... I am looking for something fresh and new... any ideas?