If Fletcher decides not to return, the logical replacement would be Alexander. But Alexander, of course, is an unrestricted free agent. And after a career-year on defense and special teams, another club could make a serious bid for his services. Alexander told CSNWashington.com earlier this month that Mike Shanahan has promised him that Redskins will make a "competitive" offer, but there's no guarantee that he'll return.
Riley, on the other hand, has another season on his contract (at a cap-friendly hit of $707,500) and appears to be on the verge of becoming a star. His total number of tackles ranked 14th in the NFL and, with another season of experience under his belt, it's entirely possible he'll crack the top-10 in 2013.
Keenan Robinson, meantime, is recovering from season-ending surgery to repair a torn pectoral muscle. The 23-year-old was injured in Dallas and missed out on critical experience as the Redskins pushed toward the playoffs. But, assuming he returns from the injury 100-percent, the highly-regarded prospect figures to see an increased role next season.