Sentry mode does not significantly increase write cycles.
Sentry does not record video. It just "moves" existing video from the recent folder to the sentry folder- which means it's only, to simplify this, updating the index/pointer, not actually writing any new files.
And the math the life cycle stuff has been shown in the past-numerous times in this very thread- even with pretty heavy usage the included 128GB stick should be good for longer than most people own a new car based on how little actual writing the system does and the expected life of flash memory.... (likewise the included stick is rated for high temps as well- though really folks should be using cabin overheat if this is a concern, the cabin has a lot of electronics after all even without the stick)