If you send an SOS message on a SPOT and want to cancel it, ...
Do you think the responsible sheriff would call off the SAR and go away with no other explanation than a Spot "Cancel SOS" message? Do you think he should? Do you think people with Spots should expect that? Do you think they will expect that? YMMV
Bee, "YMMV" means "Your mileage may vary". Comes originally from the gas mileage figures on new cars. We all know most people get lower mileage than the car makers' numbers.
DBD, a responsible sheriff would likely want to contact the SPOT carrier, that is for sure. But I would think that after receiving a Cancel SOS signal, plus maybe seeing the carrier signal an OK-Check-in, and then show some more signals indicating they were on the move, a reasonable command center would call off the troops, and maybe send a single person to meet and make contact.
I would also consider the SPOT carrier pretty irresponsible if they continued on their merry way and did not attempt to get to a location where full contact could be made to explain the reason for the SOS and the Cancel.
But as with your "YMMV" thought, we all know there are responsible people and ....not so responsible people.
BTW (By the way), that "Aspen Fire" on this side of the Sierra is the fire that caused the hikers (topic of this thread) to become disoriented. This afternoon from Fresno, we could see the plume of smoke, and it had created a huge thunderhead cloud above, from all the moisture released. Checking the web cam picture sequences today, the smoke in the Owens Valley is so bad, I feel sorry for anyone hiking Whitney today. I am sure they had a memorable (Negative) experience from all the smoke.