I'm not sure where this quote he used is from but I seen it reused so let's take a look at it. "the President of the United States and various other members of the continuity of government fell back to multiple secretive, heavily fortified locations all around the continent." So that indicates that they had a lot of places that could still be around, but maybe not because the Enclave consolidated their power before Fallout 2. But it is safe to bet that the President only consolidated American assets.
"Many members of the Enclave retreated to these remote locations in other parts of the world," indicating that the Enclave was a global force and not just an American force so that very well could mean that there are foreign facets of the Enclave still out there.
"when the bombs began to drop, they lost communications with the main group that was to be headquartered at the Poseidon Oil Rig." This absolutely screams that there are more Enclave out there because added with the previous quoted section it flat says that the Enclave that retreated to other remote locations around the world could not hear the call to consolidate after the war at Poseidon Oil Rig.
This just shows that an idea or a massive global group can't be wiped out as easily as many here seem to think and want. Plus it opens the door the a possibly well armed force coming to American soil looking for the head of their order, or at least the remnants, after they have had time to build and secure their area in other parts of the world. And it opens the door that these new Enclave invaders may have a warped or changed philosophy than the Enclave that you have seen before.
And I found this on a Wikia Enclave site.
"Enclave SigmaAfter the destruction of Raven Rock, the Enclave executed a combination of tactical retreat and all-out ?ight, and their grip on the Capital Wasteland loosened significantly. Now contending with overwhelmed soldiers, ragged Enclave camps dot the Wasteland with little communication to and from the others. With the conventional Enclave military experiencing a lack of new recruits and the high command remaining silent, the Enclave would seem to be a doomed force.
However, a small in?ux of specially trained fighters is seeking to fill the manpower losses caused by the Brotherhood of Steel's advance. Previously posted to remote and classified locations outside of the Capital Wasteland, only the most elite of Enclave personnel, trained in multiple forms of combat, can earn the right to belong to http://fallout.wikia.com/wiki/Enclave_Squad_Sigma.
Squad Sigma operates in six-soldier units, which utilize http://fallout.wikia.com/wiki/Heavy_incinerator and are led by a soldier clad in http://fallout.wikia.com/wiki/Enclave_Hellfire_armor. Furthermore, Squad Sigma members are experienced fighters, each member being a hardened veteran of numerous successful combat operations. Sigma Squads are posted around locations deemed by Enclave high command as imperative to the salvation of the cause."
This flat states that there are elements of Enclave still out there and who knows these Enclave Sigma could find a way to communicate with foreign facets of Enclave and bring the invasion.
As I have stated many times on this thread with the proper story telling Enclave could return and be believable and interesting. Should Enclave be a major player in a Fallout game in the future? Not for several games, if at all, because to do a proper story arc Bethesda would have to take time to reintroduce them and build them back up. This could only really be done through DLC content. But should Bethesda completely abandon any faction? NO! Because then you are limiting the creative possibilities of this universe and that takes away from all of us.