With SpaceX's launch cadence they could easily shift some flights. Of course you'd need a Crew Dragon that has completed refurbishment, and need to integrate it with a rocket. A month sounds like a reasonable timeline to get an unexpected rescue mission to the ISS. Which isn't great if you need a medevac, but that's why they have enough space craft docked

>On an island you can call for a boat or a helicopter.

Boat, yes; helicopter, no, unless the island is pretty close to civilization. Helicopters have very limited range. No helicopter is going to rescue you from some remote island in the south Pacific, unless it was launched from a rescue ship (in which case it was really the ship that rescued you; the helicopter was merely more convenient for transportation between the ship and the island than a tender boat).