I think that emergency satellite connectivity will add to the phone's daily power use and it's one of the reasons I carry a beacon, GPS receiver and in my safety pack power pack to recharge my phone and beacon if stranded overnight.
I absolutely agree with your choices here.
With that said my guess is that it will be a small difference in daily power use -- I expect Apple was smart enough to have this transceiver powered down when not in use.
I cannot recall the last time I was off the pavement, with no cell signal, and with no ham radio repeaters in range. So far I have chosen not to buy a PLB or SEND. This feature (when I replace my phone) will probably influence me away from a PLB or SEND, assuming that my outdoors habits don't change much.