Disclaimer:  I don't, and never have, use Sharepoint.

My thoughts are that you should have "another" back up some where.  Whether it is a Google account, on your local network, a hard drive, etc.  The reason being is, I've had what I thought to be good backups and later found out files were corrupted or didn't back up properly.

In addition: To your back up strategy, I recommend that you put in place some sort of "checking" to make sure the files that you think are being backed up are being done properly.  Don't just assume I'm backing up, so everything is fine.
I do a check every 3-6 months for mission critical data.

It is he worst thing to get to the point where you NEED a back up and find out that you don't have what you need to recover from a disaster.  (Ask me how I know)

The other thing you gain by doing this is you know what you need to do to restore your data in the event you need to.

That should be an option on your server.

Thanks!