At that point I wonder when quadcopters or fixed-wing UAVs will be feasible to at least establish visual contact with the sender of an emergency signal and/or drop off a sat-phone for bidirectional contact - there have been model aircraft capable of crossing the Atlantic [1] after all, and modern quadcopters like the DJI Matrice have something like an hour of flight time and 80 km/h speed so these could carry emergency supplies as well, no matter the terrain.
It’s already being done in a few places. But think bigger- the Royal Navy has done sea trails where they use drones to drop life rafts to sailors overboard. These aren’t little DJIs - look at the Malloy T150 and 400. The latter can also carry people and cargo up to 180kg (65kg for the former). These are in military service today with the Royal Marines and in Ukraine.
UK Border Force also uses a Tekever AR5 UAS over the English Channel to look for people crossing. It could be pretty useful in a SAR-situation though; 20 hour endurance carrying 50KG.
Think bigger also automatically means "think way more expensive". I was more thinking about something that can be placed in a small charging pod around the entrances of popular but dangerous areas.
[1] https://de.wikipedia.org/wiki/TAM_5
[2] https://www.diyphotography.net/djis-new-matrice-300-rtk-dron...