My strategy :
My primary storage is a pair of mirrored disks, which contain both my image files and catalogue.
My catalogue is backed up to an external hard drive . The catalogue is backed and integrity checked every day that I use Lightroom.
My images are also on the external hard disk, in the same directory structure as the files in the primary storage. There are extra files on the external disk which have been culled from the primary, and extra files on the primary: ones I haven't taken, and some TIFF's and such that I may not have copied across. AFAIK this would not prevent the catalogues and images working together.
I think I am fairly safe, given I don't need these to make a living, but I'd welcome comments.
I hope the OP doesn't feel the thread has been highjacked, but I think it's all relevant to using Lightroom sensibly.
Dave
P. S. I know this is all vulnerable to fire and theft (flooding isn't an issue) but that's another risk I choose to take.