Sorry for your trouble. One circuit with a very low octane fuel , thats a lot of detonation and sounds likely to ruin the engine. But immediate loss of oil pressure? That doesn't seem to connect with a short trip; quite a lot of dilution sounds like the reason for that.
The increase in oil consumption might be due to soot fouling rings, that sounds like heads off at a minimum. You could fly at low risk in a MG over the airfield for a few flights, because if the fouling was the cause, and it subsequently burnt off, then oil consumption might return to somewhat like before. It might be worth a try based on the assumption that the safety risk and the incremental damage bill are both low?