accidentally deleting the localstorage is like accidentally eating your keys (for me, at least ).
Is the app opened the whole time? If yes (and also no), may use the browser object; store your mailing list into an array and make two buttons for downloading that array locally on your device as file. Before opening the app, navigate into your filesystem, search the file, open as text and copy the whole thing; after opening the app, paste the clipboard into a textbox and import into array. May be a bit unhandy, but Ild describe this as 100% failsafe.
Anyway, a localstorage should be totally enough. Since PAX doesnt go 3 weeks, I dont think that you have to worry about clearing the storage (- or you got an Crapple product and.. well... then dont use the localstorage ).
Best regards and a nice monday,