What is the procedure when an aircraft with an emergency can't land due to a blocked runway?
What's the procedure? The procedure is, be creative to save as many lives as possible!

Really. The procedure is to determine a course of action which will likely result in the best outcome for everyone, utilizing all resources and given all constraints. Period. It is as simple as that.

There are infinitely many scenarios, and one cannot be trained for everything. However, pilots and controllers are trained to remain calm. When we look at the accident report years later, reading the document, we can easily say "if the pilots had done that, people would have been saved...". The important thing is that the people who were responsible at the time had to remain calm enough to look at the big picture instead of focusing on a particular problem, otherwise they can easily overlook a solution.

During training, it is common to throw multiple failures / emergencies together. The purpose is not to train the trainee to react to this exact combination of failure, since that is rather unlikely. Rather, the purpose is to simulate a stressful environment, under which one has to make sound and logical decisions.