Please be gentle and not call me old here...! Seriously, I was the chapter historian who really read up on the old stuff:
Phi Sigma Sigma's last year was 1973 or 1974. They were on the 6th floor, and it became the "spill-over" floor for the larger chapters who didn't have enough room for as many sisters who wanted to live there (mostly Tri-Delts & ADPis at the time).
Tri Sigma came next, and took over the 6th floor. The same year, DPhiE pretty much went under.
Kappa Delta came on campus - Theta Phi Alpha went under.
Theta Phi Alpha, Kappa Alpha Theta, Alpha Delta Pi, Delta Phi Epsilon, and heaven knows who else have re-colonized in the past 20 years to stay on campus.
FWIW, as much as I hate NOT having more sororities at Pitt, (and still can't get over Theta's demise!), it always seems that bringing in a new sorority rings the death knell for another. I would have to see at least 3/4 of the chapters making quota during formal rush, and the rest doing better at COB before I'd be in a hurry to interview a new sorority. And yes, with Kappa Alpha Theta having a house & all, they really should get first shot at it.
As we were preparing for our 150th anniversary last year, I noticed that Zeta Tau Alpha was at Pitt at one time, too - and got to meet an older alumna and the founder of the Pitt ADPi chapter. I'm sure there are more I'm forgetting. I did heard some cool stories - like that Shirley Jones (Partridge Family) used to live in the ADPi house, and the one alumna has a picture of her in her bra & panties on the upstairs phone!
honeychile