After teaching for over 20 years, former students came back once in a while. Some would talk about some good/bad experience in old days, right before I am unconsciously getting those out of my mind (which is a hard disk with limited memory space). What I really want to say is that 4 years actually amount to a very tiny portion in their entire life span. Life does go on.
In recent years, I tried (but in vain) to advise my students to see an old movie "The Emperor's Club" (天之驕子) which, in my opinion, truly reflects what former teachers like myself might have while facing students of different generations across the time zone.
好的老師從沒有自身的成就，他們傾一生之力灌注在學生的生命裡。原先他們(自以為)像是樑柱，撐起學校的一片天。建築物汰舊換新時，少有人會注意到當初的樑柱 -- But what happens if the new building proves to be a lemon good。
"A man's character is his fate."
"We are here to teach students and offer them a chance to excel themselves even against their (initial) will. Yet, some will never learn, for better or for worse. After all, teachers cannot mold students. And possibly no one can! The best we can do probably is to set up some timely examples and provide the best resources we can. The rest is out of our hands. Luckily the service we provide here does not have the life-time warranty. Otherwise, the college might go bankruptcy." If the latter is valid, MOE has no reason to care about 退場機制