I have been playing around with the tchort institute questline, and noticed the following:
1) if you are accepted, do the "Track down Rassophore Nevil" quest and leave the institute, you can go back through the main gate, however,
2) if you are accepted, do the "Track down Rassophore Nevil" quest, decide to investigate the basement, make the tchortists hostile, then leave the institute through the same vent as Nevil, you get locked out, as the main gate won't open.
Is there any other way in? Otherwise, it's not possible to progress with the main plot.
I have also tried sneaking into the basement to avoid turning tchortists hostile, but the following door is inaccessible in my game, because the cook blocks one path and the cashier the other: