Can a neck be twisted back at all? Are there tools and techniques (however expensive) that can do this
I'm talking hypothetically rather than devising a plan here
It can be honed down to a level fretboard, you can replace the original fretboard with a fretboard adjusted to the twist, you can take off the fretboard, heat the neck, untwist it and stick the fretboard back on (hoping it will stay in place). There are means to do it. My luthier experience (and the experience in the projects corner here) tells me that there is no repair you cannot do if you are willing to spend the time, money and effort on it.
I have an originally badly twisted 1973 maple board Ripper (the moldy verdisgris one that must have been rotting in a damp cellar for decades) and my luthier took off the fretboard, honed the neck ("there is enough meat to a Ripper neck", he said, though he preferred to refer to it as the "kitchen board"), reboarded and -fretted it. It now has an action lower (and buzzless) than my untwisted Rippers do.