I am curious as to what the symptoms were for him to call the spindle "Toast"? I have a 2017 Mini Mill and dread such a repair myself. I am counting on it not happening, but that is a little like gambling. There are two of us that care for the machine, but have used a few operators on it. Broke some tools, but always because of operator error and usually offset related. We do not push the machine. Not at all really. 25 to 35% max on spindle loads and those are usually from adaptive clearing. We do machine some mild steel.
If the machine isn't under warranty, it is likely a job that you could do yourself and save a little cash. That said, there may be a bit of comfort knowing that the tech may have done similar jobs before and actually knows what he is doing.