How It Was Determined Who Was In It: Despite ugly rumors that Lea Michele and Ryan Murphy did not want Dianna Agron (Quinn) to be involved in the tribute, we are told by multiple sources that it all came down to scheduling and timing. Agron simply wasn't available when the episode was shooting, and because of that, she did not ask to come back, as some of the others did. "When you write something like that," Ryan Murphy said of the episode, "there's no right way to do it. So we wrote it. We put people who were under contract to the show in it. And a lot of the actors contacted me and said, I just loved him so much can I just please be a part of it? So we put those people in." A show insider points out that Dianna attended Cory's funeral and is still "very much a part of the Glee family and remains friends with the cast."
(Snipped from this E! Article) http://www.eonline.com/news/468549/glee-s-cory-monteith-tribute-everything-you-need-to-know?cmpid=eonline-twitter&utm_source=eonline&utm_medium=twitterfeed&utm_campaign=twitterfeed_topstories&dlvrit=48939