They ALWAYS put all the astronauts onboard when they move the capsules. The reason is if the docking fails and they can't reconnect to the space station. Then they can abort and return to Earth....
Excellent observation.
Dragon is stocked with sufficient oxygen, first-aid, battery charge, rations and whatever else necessary to sustain the crew for as long as it takes to execute a weather-permitting splashdown. In space, all known contingencies have a plan B.
Is there a plan C that launches an emergency Dragon should something go wrong with the crewed-Dragon's thrusters not being able to return to ISS or execute a re-entry maneuver?
Is a Dragon to Dragon space walk feasible? The mass of moving four humans will probably require periodic thruster execution to keep them together.
Toward the end of the shuttle program, I recall scuttlebutt around an emergency shuttle launch should damage to the heat shield preclude a safe return. NASA started including a repair kit which might have been the only contingency plan?