While a couple of characters returned from the original film, they are played by different actors in this one. Only Mary Woronov returned, and while it is assumed that Doctor Vadar and Evelyn Togar may be the same person, it's never clearly stated and neither McGree nor Eaglebauer recognize her.
And the plumbing was all screwed up!
Dr. Vadar would certainly be killed by the collapse of the school building--unless the explosion kills her first.
Warning: The practical jokes depicted in this motion picture are performed by professionals. Do not attempt them at your school as they may result in DETENTION HALL FOR LIFE!