In case your BizTalk version reaches end of life it may be advisable to upgrade to a new version and migrate the current BizTalk applications to the new version. Yet end of life of BizTalk Server does not perse have to be the driver for an upgrade. There
can be other reasons for an upgrade like complete upgrade of the Microsoft platform or parts of it. For instance an enterprise may want to upgrade to an SQL Server version that does is not supported by BizTalk Server. This will lead to an upgrade of BizTalk
and possible other server products.
Another important place to find a huge amount of BizTalk related articles is the TechNet Wiki itself. The best entry point is
BizTalk Server Resources on the TechNet Wiki!