I think its interesting that they fell out over John Mark. Over a matter of personnel not of principle or doctrine. I have seen sharp disagreements that started as matters of personnel or personality clash that, in subsequent years, hardened around doctrinal themes. But weren't that originally. When we see major disagreements between believers in our generation over apparently doctrinal themes it is always worth a quick check back to see how and where they emerged, and whether it was always doctrinal. Trying to figure out how to put the wheels back on the wagon may be easier if we figure out why they fell off in the first place.