I understand that this particular plane has been for sale for a while -
maybe a year. Definitely gives me pause, but the price was much higher
then.

How many TTAF hours can someone reasonably expect from a trainer C172?
Looking around at the ads, I do not see many hours above 10k. I guess
if I knew 20,000 TTAF hours was okay, and this plane is just
middle-aged, then I might consider keeping it longer. However, the FBO
has told me that in 5 to 10 years, they expect to no longer carry
C172's, since they already have many more 172SP's, which are taking
over.

Since I got my private thru the same FBO, I trust them and the people
there a good bit. At this point, the leaseback is probably the least of
my worries. Of course, having a stranger flying my beater airplane is
probably better than having a stranger flying my nice new expensive
172SP!

Jae