the ESB should not be so rigid that it should hang in the case that this happens.
I actually agree with the "hanging is bad" point. In fact, there is a jira on this, which - per your tone you might find surprising - I am actually working on right now:
https://jira.jboss.org/jira/browse/JBESB-3172
My belief is that it is not bad for the service to FAIL with an Exception. I do believe that it should not hang, however, thus the jira item above.