I’m not an engineer but I have been wondering why they could not use a plumbers plug for a temp stop until they drill new well vents. A long plug maybe 50 feet long made of flexible hard rubber about six inches in diameter. Shove it down the well pipe and expand the plug with air or a material that will withstand the pressure down there.
The first thing that needs to understood is the inability to get anything past the BOP, if you can get past the BOP you can plug with cement.