Know that slo-mo moment when you wish you could take back whatever you've just done? After turning on FileVault (which kicks off a restart) I belatedly realized a restart from a Safari update was also pending. BIG mistake. What I learned: never leave a restart pending, or if you DO, don't forget about it. Now, I HOPE my little old (2012) Mini has recovered. I thought I'd have to reinstall OS X. Recovery Mode DID have some sort of image ready for me (I think). But I didn't know what to do with it and nothing was happening automatically. I think (I hope, I pray) Disk Utility Repair may have done the trick.