I don’t think the average users ever delete any of their browser data. In this case however, the whole idea would be that there is redundancy and it is ok for you to clear your cache and storage. As for the hoster, they would probably use a nodejs type server to host their files instead of relying on having a browser tab open.

However, I do agree that relying on regular web browsers is not a good idea. A browser update could limit resources of background tabs even more than they normally do and soon your application is down.