If you can (a) keep out of accidents severe enough to damage the unibody, and (b) avoid rusting out the car, the answer to your question is “the car can be kept alive indefinitely.”
There are certain parts (engine, transmission) that wear predominately on miles. They can all be replaced as needed. Also, all of the rubber parts wear on the basis of age (and possibly miles, too). They are also all replaceable.
What generally happens to a car that gets up around 10+ years old and 150,000 miles is that “something big” fails (like a transmission or engine), and the owner realizes that the repair costs meet or exceed the “blue book” value of the car (so s/he scraps it).
However, you represent a special case: because of your daughter, this particular car has a personal value to you and her that will be over and above the “blue book” value as it ages. Thus, you may well decide to spend $2,000 on a repair to a car with a $1,800 “blue book” value. (Remember that such valuations only matter if you intend to buy and/or sell a car.)
Collectible cars with unusually high “hull values” can be kept alive a long, long time. Not too many '64.5 Mustangs being scrapped because of bad engines!
(You might, however, need to “stand strong” about fixing a car when a mechanic tries to convince you “it isn’t worth fixing.”)