there is no drm on itch's side. if the developer did not do some drm or login/online requirement, games cannot be removed from your computer or be bricked.
the license stays. it says so in the terms. https://itch.io/docs/legal/terms#4-publisher-content
but the elephant in the room is this: there is no guarantee that the files will stay downloadable. devs can delete their pages at any time. it is unprofessional to do so, but this is itch and most devs here are not professionals. there was a case with a rather successful game last year. i do not recall the name, but i think they released it on another platform that required them to remove it or any such crap.