I agree Theta Sig AGD, I would contact NIC (
www.nicindy.org) and ask about that. I'm pretty sure if you "disassociate" you wouldn't be able to use the Sigma Tau Gamma letters and you'd have to return your charter (if this is even possible) and I'm almost 100% positive you could never belong to another NIC fraternity if you ever wanted to (unless you were not initiated).
I know the issue is going Local, but if you did that, Sigma Tau Gamma would dissappear (the national organization would not let you stay as STG's, they'd take that away, although you would feel you are, if you disassociate, the national organization would no longer be liable for you, hence you must lose all contact/association with them).
On a side note, about housing? Do you know for a fact that it's the National organizations responsibility to update housing for it's chapters? Coming from a past HQ staff member here...housing is one area that organizations try to stay away from because of liability. I doubt that Sigma Tau Gamma has a huge housing fund where they just update chapter houses and buy new one's all over the country. I'm pretty positive that that's up to your chapter and your alumni.
Good luck, I'd suggest if you want to see Sigma Tau Gamma on your campus in 20 years, then stay with your nationals...and if they are misappropriating funds? Someone will catch them...but I doubt that's the case (they can buy a 7 million dollar pavillion, it's perfectly legal and no misappropriation of funds...it was probably just something that the executive council thought was good for the fraternity).