I have some experience with handling a case where no standby service was available for my pet. I know pets are not humans, but I think there is some insight worth sharing.
If you can source dry ice, you can use this as a substitute for liquid nitrogen for about 6 months without suffering too much degradation compared to liquid nitrogen. Generally, you will want to opt for this if you cannot arrange for transport to a storage facility within 24 hours of clinical death. About half of all cryonics cases are “straight freeze” with no cryoprotectant, so there is a good chance methods will be invested in to revive those who undergo a straight freeze.
My pet passed away suddenly two years ago after a failed emergency surgery. I had her immediately transferred into ice-water bath after we could not restart her heartbeat. About 19 hours later I arrived with a source of dry ice to straight freeze her until I could arrange transport to Switzerland for storage in Tomorrow Bio’s facility. I held her in a dedicated freezer with dry ice (replenished every other day to every two days) for about a month before I could work out how to transport her to Switzerland.
From my conversations with Emil (CEO of Tomorrow Bio) this is very similar to their own procedure (as my pet was already under anesthesia from the surgery) minus the cryoprotectant. So if you can have someone act quickly to cool your body to close to freezing then get you in dry ice for extended pre-liquid nitrogen storage you won’t be much worse off than the other straight frozen cases.
For disclosure, I am signed up with Tomorrow Bio and this is my plan if my imminent cryopreservation is needed. I live in a country with no standby service but figure this is better than nothing.
The main thing you want to prevent is large scale ice crystal formation. Dry ice sits just below the temperature needed for water to crystalize when freezing, so it delays the crystal formation by a substantial amount. However, for extended periods the ice can still crystalize so that’s why it’s important to get to cryogenic temperatures.