Stan Lee may not be appearing at the Wizard World Ohio convention, or at the Authors! Authors! festival he was set to appear at during the same time period, but his Twitter account didn't go dark on Sunday, retweeting a message from Todd McFarlane as well as posting a photograph of Lee with Supernatural star Micha Collins, complete with a joke about wanting a cameo on the popular CW series.
When an 89-year-old man, especially one who means a lot to a great number of people, abruptly cancels a number of plans, it's natural for people to assume the worst--but so far, there's nothing to suggest that Lee is in poor health, that anything has happened to his immediate family or any of the other worst-case scenarios fans have been imagining for the last couple of days.
In Wizard World's words, the organization“were informed by Stan Lee’s management that Stan would be unable to attend any upcoming appearances for the near future.” That's a nicely vague sentiment, one that allows for a lot of interpretation.
Earlier in the year, Lee canceled a number of public appearances, citing the death of a business associate and exhaustion from all the demands on his time around the release of Marvel's The Avengers in early May. While there hasn't been another promotoional push that big since, Lee is certainly still in demand, with confirmed cameo appearances in Iron Man 3 and Thor: The Dark World. He also recently shot an episode of Kevin Smith's Comic Book Men for AMC.
The organizers of the Dallas Comic-Con have also reportedly told fans that Lee has "re-confirmed" to appear at their Fan Days, where he was scheduled to appear the third week of October.
Lee's promotional calendar is always full, and he seems to be shooting something or another for the Stan Lee's World of Heroes YouTube page pretty much every week--so look for an update sooner than later, as more cancellations are likely to concern fans and if there's no need for them, Lee's people will likely feel obliged to put the comics community at ease.