Nothing needs to be feared in crypto, because everything we do must have risks. Because the possibility that happens a little if we save coins in the wallet online and at one time the site will disappear, actually I am not afraid because there is no way that could happen.
Who told you the possibility is little. please try and research before you make ill-informed information. Online wallet do not backup your private key.
This is also incorrect. Any online (hot) wallet worth their weight in salt will back up this information. That doesn't mean they'll give it to you, but in order to spend your funds (or let you spend them) they definitely need it.