You DON’T rebuild a crumbling, rotting edifice. You’ll BULLdoze it and start fresh. Hire a NEW architect, devise new building plans, use the best construction materials and methods, and move in!
When you bulldoze everything you run the risk of ruining what is “right” with the party. I think it might be easier to rebuild rather than starting from scratch. Use the foundation that is already there, and re-model the rooms of the building that don’t work.