Let this be a lesson on building to suit your environment. I love that part of the world but would I build a straw bale house there? Or earth-bermed? Or (yadda yadda). If I lived on the wet coast now I would build a rammed-earth home or "light clay" - a gorgeous formed clay/straw building method. But not underground. I'm sure there are successful examples currently out there, but will they still be that way 40 years down the road? Best of luck!

I'd expect the excavation costs to (carefully) unearth the home and cover it 100% with EPDM to easily cost more than the home is technically "worth". Not every decision is 100% about return on expense though.

Some people like hobbies and it keeps them occupied. Some people fall in love with "saving" a home, even if it's a huge expense for no gain.

If you don't want to spend the money, bulldoze it and build something else. Probably for less than the repair.