For remote kayaking, I never go with a group of fewer than four people. The most likely reason we'd be unable to paddle out would be a dislocated shoulder. With four people, we'd have two to paddle out to get help and one to stay with the injured person.

The big situation I see which would prevent SAR from reaching us would be severe flooding which forced us away from the river. In that case, our best bet would be hiking to the takeout - not fun in rough terrain and paddling booties! Fortunately, the maximum hike should be less than 15 miles. That's about the maximum distance I'd want to paddle for a daytrip, and we could probably hike out in a few days. For longer trips, the group would have substantially more gear - like sleeping bags, tents, and footwear!