This means that Oliver would not even tinker with the idea of bringing back his loved one from the dead via the Lazarus Pit in Nanda Parbat, the way they did with Thea Queen, played by Willa Holland in Season 3, and Sara Lance, played by Caity Lotz, in the current fourth season.
According to some speculations, the character who would most likely die in Season 4 of “Arrow” is John Diggle, played by David Ramsay.
Despite their occasional differences in opinion most of the time, John is very close to Oliver that is why he shed a tear.
But there are also speculations that it could be Captain Quentin Lance of the Star City Police Department. However, if it was Captain Lance, Laurel Lance should have been with Oliver in the tombstone.
Rumors also suggest that it could be Malcolm Merlyn but he is Ra’s Al Gul and very difficult to be killed. Besides, he is one of the most interesting characters in the TV series and the show can’t do without him.
However, because of the presence of Barry in that tombstone scene, and no other members from Team Arrow, it is possible that the character that Oliver is crying for is his son that only he and Barry knows, including the mother of the child.