My son had a pee emergency right before riding Tower of Terror. The CM that directed us to the chicken exit handed us fast passes so we could quickly get back in line after he went pee. I thought that was nice. As other's have said, some lines are easier to rejoin than others and you just do what works at the time. My son had to leave the Play House Disney line. They arrived back just in time for my husband to hand him to me over the rails. My son got to sit down with me, but my husband ended up standing in the back. We've also done the hand over the rails trick and sneak back in for the Astro Orbiter during a pee emergency. The Bugs Life pee emergency though was a total wash, my son and husband had to skip the whole show while the rest of the family watched it. These pee situations worried me a lot leading up to the trip the first time we went without diapers, but when they actually happen you realize they are not a big deal, and were hardly worth all the worry. Things just work themselves out. Don't worry too much!