As the customer have a Red Hat subscription they might ask the support direct .
You can have a look at the Red Hat support policy
AS4.3 has only Mantenance Support until Jan 2013 (4.2 is outdated)
AS5 Full support Nov 2012, Maintenance Nov 2016
AS6 Full support Jun 2016, Maintenance Jun 2019
Under a special subscription you might have 3 extra years 'Extended Life support'. But remember Maintenance/Extended is only for limited bugfixing.
So it is on the customer, if you use AS5 you might run into an issue where you have the need to upgrade for features (i.e. EE6).
To answer ayou question, if you find such a blocker and it is a bug it will be fixed until Nov 2016.