As I recall, I was in the same boat as you, but fortunately had a Recovery made with DiskMakerX on a thumb drive. Once that took effect, I was the able to at least restore.
Sorry my help is not much.
No doubt others will have better counsel-
Harv 27" i7 iMac (10.13.6), iPhone Xs Max (12.1)
Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
