For protection, I put all my files I care about on Dropbox. Is that enough? It's enough for backup for most things, but I worry attackers would be smart enough to kill it and also the old revisions that Dropbox stores.
For mass deletes that are cumbersome to recover using Dropbox's interface, that article mentions you can contact customer support to get assistance recovering from mass deletion events.
Turns out that me being annoyed means I now have a fully intact version of the data and nobody had to pay anything.
But if you are a concerned customer, why don't you just head over to their help pages and see what the features and limits regarding history and file deletion are?