Trolman, for the love of scenario and making this War a little bit more fun you can allways betray us and join the old gods... what? I'm just saying...
Okay, seriously, since Old Gods have enough faceless ones and those goey things, they already might start a war with you by themselves, but they can't convert all people at a time, first they'll take over the land, then kill you since according to pact you are the only one who can control the converted people except them, then they are gonna make all people uglier than they were before... s this is what I recommend for you: or escape to Draenosh and try to defend here, or hide in Azeroth and start a guerilla warfare with Old Gods!