if ı buy do ı get every update or shuld ı buy again or download again
and yes ı didn t use itch.io before
Once purchased, you don't have pay again for updates. The game doesn't update itself like Steam so you will need to download it again once an update is dropped.
Is it destroying the save ?
You will not lose saves as long as your Windows drive is not erased. Game save may get corrupted if I remove some values from save data.
