Microsoft's Threat Management Gateway (TMG), the successor to our old friend ISA Server, is on its last legs; we've known that for quite a while. Microsoft announced its impending demise just over three years ago in September 2012 and discontinued mainstream support in April of this year. Despite the terminal diagnosis, they don't plan to pull the life support plug (extended support) until 2020.
Many companies continue to rely on TMG for their perimeter security in the meantime, but that is likely to change as it wastes away, losing functionality for which it was once famous. In a few short months, Microsoft will be discontinuing the Microsoft Reputation Services (MRS) for URL categorization. As of January 1, TMG will no longer be able to use this service to do URL filtering and Network Inspection Service (NIS) updates will cease.
If you were counting on riding TMG to the end of life date for five more years, you might want to rethink that plan.