Many years ago I rode almost a 375 miler with 4 very experienced riders and we had a very steady pace-line most of the time (about 5min pulls). The route was flat and it was very easy to keep the pace line. I do not remember the average speed, but because of the pace-line it was way higher that other people riding single.
I also rode a 1000 km on a different ride and one rider pulled almost 90% of the entire ride(4 of us). He just could not sit in the back and rest, may be just for a few minutes once in a while.
It will also depend of the terrain. If the route is hilly, the pace-line will not work, riders will be climbing at different rate, especially after a few hours of riding. It may be more important to ride at your own pace. If it is important to keep a pace-line, it should be as slow as the slowest rider, so he or she could keep up.
200 miles is a long ride, the fatigue will set in eventually and the difference between the rider fitness and endurance will get bigger with millage, so the captain should decide how to ride it.
I would probably plan on riding as a pace-line initially, providing the ride is not hilly, but later on in the ride the team may split and ride at a different pace, just to gather at pre-planned places(if need be).