Undergrads are a different story, but can provide great cashflow in shared environments if you are prepared for the management issues.I could probably expound on the Logan (and Cache Valley) market indefinitely.  

At which point I would either continue doing the same thing over and over indefinitely, or sell all my assets as a portfolio loan(or as a few sets of), and then roll all that pooled money over into a single larger asset IE: a large apartment complex, where ever the CF be best at the time.

And every once in a blue moon you can find one with an indefinite hold period. 

However, capital gains tax will be assessed as the payments are received by the seller, unlike a 1031 exchange, whereby the capital gains tax can be deferred indefinitely for the exchanging individual.

But no one can lose money indefinitely. 

Well one of them wants to leave indefinitely.  

I left his rent at $900 for the past 2 years, and hope he stays indefinitely.  

But, the property also had significant positive cash flow....so we didn't mind holding on to it indefinitely.

You can do what is called a section 1031 exchange and defer all taxes indefinitely.

As far as the exit strategy, I think the goal is to hold indefinitely.