"Regular" licenses do not expire, so this shouldn't really be a problem. But I do agree that if something like this happens, it should give some kind of warning to the site owner before affecting the end user.
The error itself is only injected html/css, but can affect functionality when it's injected at a bad place giving. Have seen it injected in css/js-files which has caused the site and edit mode to be unusable.
Per Nergård blogged about a scheduled job that sends email notifications when the license is about to expire: http://world.episerver.com/blogs/Per-Nergard/Dates/2015/10/monitor-when-the-episerver-license-expires-/
EPiServer displays a warning when the license is expired, like Sas.no earlier today. See tweet from https://twitter.com/Haakon89
If the license expires why display it for the user to see, isn't it better to display the warning for the admins and editors to see?
Does EPIServer warn you about license about to expire? not?
What are the best practices for handling the EPiServer license? To keep them valid at all times.
A side question, does the expired license cause any trouble for the EPIServer functionality?