I see that this is a best effort service, and I’m not trying to be overly critical, but I would think your best effort could involve not displaying links that lead to no content. Can’t you check that with the API?
I think the "best effort" no guarantees thing is due to Twitter and how they deal with API users like this. They have a reputation for shutting down 3rd party extensions so if more than 50 people use this in a 24h period they get suspended for example.
You may want to add some graceful errors for users not found