They probably won't like it, but worst case scenario is - not that they leave, which is probably what you'd prefer - but that they stay and now all of a sudden they want you to fix everything.  

Suddenly my second child's severe hearing issues didn't warrant ear tubes.  

A great example is that just as granite has come down in price to be more accessible it's suddenly out and synthetic tops are in.

All of a sudden they are complaining about all kinds of maintenance issues, you end up in and out of the apartment a bunch of times with them complaining about pests and mold and funny smells or noise - you name it - instead of just asking if they can break the lease.So, I'd start there. 

rents go down people paying 800 all of a sudden can move to a nicer home.. the 800 rent gets lowered to 600 so its not vacant.. ??

If you catch them off guard after they've become comfortable, you can often learn what's really going on, or you can see that they all of a sudden don't get eye contact or they blurt out something they didn't intend to share like, "My aunt doesn't want me sleeping on her couch anymore," etc. 

I can't see a plausible reason why having this guy move in would suddenly cause your tenant to go off the rails. 

She’s all of a sudden sick and is unable to work - this was her excuse after she told me she’ll pay April’s rent by the 25th. 

She initially stated she would move out after 30 days but suddenly decided to leave tomorrow.  

And then, if the university's vast real estate holdings, including lots of properties around the perimeter of the campus that is used for housing or just simply for investment purposes, all of a sudden crash in value, then what happens to that town?