Yes. When O has given a fee simple determinable and has not given anything else afterwards, then O has retained a possibility of reverter. The fee simple determinable need never determine, of course, so that the particular reversionary interest retained by O is only a possibility.

To check to see if you understand this:

O conveys to A for ten years, then to B for life, then to C as long as the land is used for agricultural purposes. Give the state of the title, that is, without having multiple choices, write down (don't try to remember: write down on paper, archaically) all the interest holders and what each one has. When you are done, click on "answer" to see if you are correct. Remember to state both the estate and kind of future interest.