As long as whatever fuel your using didn't die, it should be ok. It sounds like it hit a stall. I've had pork butts drop in temp during stalls as well. Either way, the roast is fully cooked at that temp, it's just not broken down enough to pull yet.
You're on the way up, so that is a good sign. It sounds like a monster stall. If you're tired of manning the smoker, you can foil and finish in a 300 degree oven, it will make the bark a little mushy, but you won't lose any discernible taste or tenderness. I made 3 roasts that way 2 weeks ago, and did 2 roasts like that today. They still come out great.