Getting out of line and getting back in could be rather tricky, actually. The queues at WDW are very windy, going back and forth inside the attraction building. You'd be squeezing past dozens of people (maybe even a hundred?) and some may not let you past, especially if they did not see you get out of line in the first place.
How long do you think it would take to get to the bathroom, use it, and get back? I'm thinking at least 15 minutes, as the bathrooms can be crowded, with queues of their own, etc.
Your best bet would be to keep in touch by cellphone with your family - that way, they could let people pass them in the queue so that they wouldn't be too far into the building for you to easily catch up.
BTW, I'm another gall-bladderless person, and have had similar issues. This will be my first trip to WDW since having it removed, and I'm hoping it won't be too bad!