Warning! The following contains spoilers for the Arrow episode "The Thanatos Guild." Read at your own risk!
Arrow fans were warned that the return episode "The Thanatos Guild" would change the show forever, and it certainly did, with major character Thea Queen leaving the series with Roy Harper and Nyssa Al Ghul to track down three remaining Lazarus pits that remained in the world. Fans may have been surprised by the departure, but for Arrow's cast and Marc Guggenheim, actress Willa Holland's leaving was a long time coming. Guggenheim went into detail as to why the show said goodbye to Thea, and why this might be the last time fans will see her in the series:
Willa Holland's desire to have a life outside of Arrow hasn't been a huge secret to fans of the show, and Marc Guggenheim and others have been pretty upfront about why her presence has dwindled in past seasons. Guggenheim went on to say that while he and the writers would've loved to have Holland stick around as Thea, he understood that after five-plus years on Arrow, some actors are going to want to move on and do other things.
Marc Guggenheim gave zero hints of ill will towards Willa Holland's decision to leave, and judging from his quote, it's not as though the crew was completely blindsided by her decision. In the end, both parties came to an understanding and the writers were able to give Thea a proper exit that satisfied both Holland's wishes and gave fans a rare happy-ish ending in Arrow. Plus, Roy!
Thea's ending definitely set up the possibility that she could one day return to Arrow, although Marc Guggenheim said that decision is really up to Willa Holland herself. Thea's open ending may have been crafted so the Arrow writers could leave that door open should Holland ever wish to return, but more likely than not, fans got a peaceful ending because Guggenheim has been adamant throughout the show's run that he would never kill Thea Queen. Guggenheim expressed that once again in his interview with EW, and said that while many endings were considered for Thea, death was not one of them:
For now, Arrow will press on without Willa Holland and air on The CW on Thursdays at 9:00 p.m. ET. For a look at other superhero shows that are making their way to television soon, visit our superhero premiere guide. Those wishing to see a full picture of what television shows are premiering in 2018 can find out with our midseason premiere guide and summer premiere guide.