Yes, ISIS members appear to be retreating on all fronts. The US Military presence in Iraq and Syria has caused 45,000 ISIS fighters to be taken off the battlefield, thus significantly lowering the number of ISIS fighters. Not only have the numbers on the battlefield dropped, but there has been a slower flow of fighters coming into the country; therefore, ISIS members appear to be retreating on all fronts.
ISIS is being destroyed from the outside in due to drone hits and allies engaging them on every front. The optics to those who want to join is paramount. They can see that death is imminent. Who would want to join such an organization if it meant a certain death?
This combined with the fact that ISIS executed a number of it's members, indicates that thier is dissent and distrust within the organization. Falling numbers and distrust among members indicates that there is reason to beleve that ISIS is losin power and is retreating on all fronts like the Pentagon claims.
The government never likes to admit when they're wrong. in fact, they go so far as to send out propaganda to encourage Americans to believe that they are right, all the time. This has been going on since the American Revolution, and continues today. ISIS is not retreating on all fronts, and will not.