WARNING: This article contains SPOILERS for Arrow's season 7 finale.
The final episode of Arrow season 7 confirmed what had been long suspected - that Oliver Queen is destined to die during the events of Arrow season 8. While this had long been suspected ever since it was announced that the long-running superhero show would come to a close after 8 seasons, it had yet to be confirmed until now.
While the exact circumstances of Oliver's death are a mystery, it has been known for some time that Oliver Queen wasn't going to live to a ripe old age. The Arrow season 7 flash-forwards sequences, which have made up a major portion of this season's story, confirmed that Oliver Queen didn't live for too long. Indeed, his daughter, Mia Smoak, grew up not knowing her father, though it was shown that Oliver was there to see his daughter's birth.
The flash-forwards in"You Have Saved This City" further narrowed down the date of Oliver Queen's passing. Near the end of the episode, Felicity Smoak met with her children, Mia and William Clayton, in what had once been the backyard of Queen Manor to honor Oliver Queen's legacy. They meet by what is revealed to be Oliver Queen's tombstone, which notes that he died sometime in 2019.
Many fans also theorized that the Emerald Archer's days were numbered after the 2018 Elseworlds crossover event, where Green Arrow made an unspecified bargain with the cosmic being known as the Monitor to save the lives of Barry Allen and Kara Danvers. The final modern day scenes of "You Have Saved This City" seemed to confirm this, as the Monitor appeared before Felicity and Oliver in their living room. He simply nodded when Oliver asked if it was time.
The full details of Oliver's bargain were revealed, when Felicity balked as Oliver said he was about to go away for good. In exchange for saving The Flash and Supergirl, Oliver had agreed to help the Monitor in preparing "whatever the Multiverse requires to survive the crisis that is looming." The Monitor confirmed that Oliver was destined to die in the battle to come but said that there was nothing he could do to prevent it and the most that could be hoped for was that Oliver's death might be used to save countless other lives.
This was cold comfort for Felicity, who was revealed to have made her own bargain with the Monitor. The Arrow season 7 finale concluded with the Felicity of 2040 meeting with the Monitor and affirming her commitment to making a journey she could not return from and stepping into a breach with the Monitor. Precisely where they went is open to interpretation, but it's presumed that wherever Felicity and Oliver wound up that they are together. All that remains now is to see how Oliver Queen dies a hero's death in the upcoming Crisis on Infinite Earths event.