From the books prospective, I believe you restart P1 if you're gaining weight back and you aren't controlling it anymore...
You have the special event coming up.. you can plan for. Have an idea of before, during and after. Have it down that after the event, get right back on track. Even if that means dropping some of the ww's and what not a little bit.. but don't necessarily have to go back to p1...
I started p1 about 3 weeks ago. DH and I goofed off during the first try and then my grandma died. Since we never made it out of p1, we just restarted it... but that's different than if we'd goofed a little bit and then been off for a few days with the family and then jumped back into p2...
its everybody's body and circumstances..