Webstorage and Cache

I know about Webstorage and the basics on how to implement it. My question is what happens when the user decides to clear out his/her internet cache? Won't that delete the Webstorage info and thus wipe out all saved info in the process?

Is there a way to backup the Webstorage data somewhere else on my internet server or on their machine so it can be retrievable?

My project Way of the Sax (I'm sure you all know about it by now) is a very lengthy interactive comic that requires save points due to several features that include minigame and collection scores and reader decisions.

Is this what requires the AJAX plugin?

It's easy to test: just store something in WebStorage, clear your cache, and see if WebStorage is still saved. Different browsers might treat it differently though.

Even if it gets cleared, I wouldn't worry about it: 99% of ordinary users probably never touch their cache.

I�m just curious, is there a way to backup the data then upload the data on game if want to continue the game?