I just can't see the world ending from things such as wars or viruses. Those have been happening for thousands and thousands of years. Out of all the reasons you listed I think the most probable ones would have to be the asteroid or sea levels rising.
Who's the best Pac, Nas, and Big. Just leave it to that.
PLAYSTATION®3 is the future.....NOW.......B_E_L_I_E_V_E
Slaughterhouse Is The Sh*t .... NOW ........ B_E_L_I_E_V_E