Added text in Section 6.4 explaining what other actions should be taken when a
messaging association fails:

                              ................... If a messaging
   association fails, this MUST be indicated back to the routing state
   machines which use it, and these MAY generate indications to
   signalling applications.  In particular, if the messaging association
   was being used to deliver messages reliably, this MUST be reported as
   a NetworkNotification error (Appendix B.4).

From Adrian Farrel:

Section 6.4 
er_MAFailure is not possible in Awaiting Connection state. 

Section 6.4 Rule 8 
Should there be some feedback to the Message State machines 
or can we rely on them to fail to find an MA next time they 
try? What about potentially lost messages?