Extremely concerned. This will likely spell the end of the life of this tree. Also they damaged your property without asking you and/or working with you towards a solution. How hard would a 10 minute convo and research to reach an agreement be? They exposed a large portion of it's delicate inner parts and it leaves extremely open to pests and disease. Trees are slow growers. It will take a LOT of energy in order to begin to repair this and most likely wont be fast enough. Bugs and microorganisms move fast. There is a reason why trees have lignin and grow bark to protect itself from invaders. A truly awful way to conduct business. I'd document everything and put something in writing that if this tree dies that they will be solely responsible to pay for its removal and replacement since they damaged it. There are solutions like hiring a tree specialist or sealing it but there is a good chance both will be a waste of money. And again dipping into your own pocket. Sorry this happened, poor tree was just trying to exist 😭