They have to choose something other than medium though. At the very least they are guaranteed track position with a tyre that should take them to the end.
That would've been a huge risk, earlier this race you saw that the mediums only lasted about 17 laps, and they had almost 24 to go if they chose soft. It's honestly amazing Russel was able to keep the soft from degrading for the rest of the race, but it was a huge risk and probably a bit of luck. Even Russel said it was ambitious