The letter does make it sound as though termination is just a matter of taking a formal vote to make it official, but you said you have new info that is somewhat hopeful.
I have a family member who saw this happen with his fraternity, which was right on the brink of being removed from campus. He and some other alums banned together, and with the help of some actives who really wanted to save the house, they did pull it out of the fire. It was a lot of work and took several years before the fraternity was fully restored as a strong chapter, but they did save it.
As AOII Angel pointed out, though, this may be tied in with the culture of the campus This could mean the problem is bigger than just your chapter. Your nationals say the current culture of the chapter can't be reversed, which makes me think the overall environment is not ripe or supportive enough for the chapter to be restored. This is always difficult and disappointing to see.
Best of luck -- I hope there is a doable plan of action and an opportunity for resolution.