Joey,
I was a building contractor for 25 years. I WOULD NOT FIRE HIM. By firing him your letting him off the hook. First off, the engineer he hire is hopefully, licensed and insured. I would assume that the contractor himself is licensed and insured.
I think you need to have a list of corrective made up by your engineer. The contractor needs to do the corrective work under the supervision of your engineer, at his own cost. Cost of engineer supervision and construction. At this point he either does the work or he quits. He'll most likely quit.
Now, you have a very solid claim against him. Defective work, abandonment and breach of contract.
Him quitting after he screw everything up is much better than you firing him!!
Than, you can go after the contractor and his engineer.
I have never seen a building that was un-repairable. I love to build condemned buildings. There the best deals and can always be fix. I have done 3 in the last 4 years.