What's more redundant than having a copy of the file saved across every device you own. It's not like the information is lost if dropbox's servers go down for a short period of time. I've never had a problem with dropbox, so far in my eyes their track record has been good. The problem that Google will have is that Dropbox is extremely simple, that's what it has going for it. The simplicity of folder synchronization is going to be hard to beat in my opinion, unless they copy the model.

They will keep your data, redundantly, forever. Only your account and access to your own data (including gmail) will be kaput.