TNT is more forceful than most mine trains and has required a lot more maintenance to my knowledge than most of its type. They have had to essentially retrack portions of it several times, and at one point in my memory they replaced the headers and some supports. S&S is still servicing Arrow stuff, but the company has changed hands so many times you wonder how they are doing these days.
In any case, TNT's tunnel section has been a sore spot for years now and I'm guessing a real fix won't be cheap. Not to mention the jarring turn before the lift hill. It's been a source of injuries and lawsuits I'm sure.
Will be another major kick in the childhood as well as coaster history to see it go, but out of all the classics SDC will have removed/replaced at that point it will be one of the most understandable.