Warner Bros. Television, the studio which produces ER for NBC, kept Dr. Ross’s cameo in “Such Sweet Sorrow” a secret from NBC, which promoted the episode as Carol Hathaway’s goodbye, with no mention of Dr. Ross’ appearance. The original version of “Such Sweet Sorrow” that Warner Bros. sent to NBC ended after the scene where we see Hathaway on the plane to Seattle. At the 11th hour, Warner Bros. messengered an “edited” version of the episode to NBC headquarters in New York for broadcast — NBC had no time to preview the episode prior to airing the extended episode in which Clooney appears. NBC was miffed that it was kept in the dark as it could have generated valuable ad revenue if it had aired promos that the episode marked the return of George Clooney. Clooney cited the fans of the show for his reason for making the cameo (he wanted Hathaway and Ross’s characters to get back together, which many fans hoped for). Clooney reportedly only asked to be paid scale for the cameo.
In the 11th season finale “The Show Must Go On” Dr. Ross was briefly shown in a photograph as part of a slide show at Dr. John Carter’s farewell party.
In the season 14 episode “Status Quo”, Jeanie Boulet mentions Doug and Carol when she returns to the ER. Nurse Haleh Adams states that they are living happily in Seattle and that their daughters are now in 3rd grade.
In the Season 15 episode The Book of Abby, long-serving nurse Haleh Adams shows the departing Abby Lockhart a closet wall where all the past doctors and employees have put their locker name tags. Amongst them, the tag “Ross” is seen.
In the season 15 episode “Old Times,” Doug is working as an attending physician at the University of Washington Medical Center. He is helping a grieving grandmother (Susan Sarandon) whose grandson was gravely injured in a bicycle accident. He talks to Sam and Neela after finding out they are from County, asking them if any of his old colleagues still work there. Doug and Carol are responsible for getting the kidney for Carter and a heart for another County patient, but they never discover who receives the organs.