But I wonder if there would still be something more elegant than the every-other-line error checking shown in the article.

Factor out the error checking into a function:

    onerrexit(is_numeric($id), 'The ID is not a number.');
    onerrexit($db = open_database(), 'There was an error connecting to the database.');
    ...

I admit you still have to explicitly state you're checking, but that's not much overhead, makes the code somewhat clearer, and gets rid of all the if(...). If the error-action is more involved, like your "third paragraph", then you can make an errcheck that takes a function reference for the error-action instead (not sure if that's possible --- haven't used PHP in a long time --- but there's probably a similar method otherwise.)