Revenue tickets have different rules depending on the fare. A full fare ticket is not lost if you no-show.

Check out this page: http://www.united.com/page/article/0,,1141,00.html

The applicable condition (in my opinion) is: "Ticket validity: Awards are valid for one year from the date of issue. "

There is nothing in these terms & conditions that says the award is forfeited if you no-show.. you just have to use it within 1 year of issue.. or pay the fee to have the miles credited back.

I would probably keep the award reservation in place for the elite who is not flying.. but I don't think it's necessary to check them in.. it isn't likely the E+ seat will be taken away from the other traveler.