First, my friend, until and unless there were a single stable government for the entire earth...which I do not see happening any time in the next many generations (at least in my faith until Christ returns at which time we will no longer need any instruments of war), there is no way there will ever be a single class carrier for the whole earth.
The closest we have to that is the Nimitz class...and now the Ford Class for the US. They represent over 90% of the nuclear carriers, and 100% of the Super-carriers on earth and the ten nimitz are a single class, and the Ford's which replace them will alao be one class.
Second...no, They will not go alone.
Such a huge, expensive, and critical assett will never go to sea (or later, IMHO, to the stars) alone. With the technology available, there will always be people or nations designing smaller, heavily armed combatants, who cannot afford n investment like that, who will seek to neutralize it should it ever be used against them.
Lasers, rail guns, nuclear missiles, etc. all can be mounted on smaller platforms. Newer varities of torpedoes and other sub-surface weapons. A large capitol vessel like a carrier will always need smaller, less expensive, well armed escorts to stand between the large vessel and those threats. I just do not see that changing in the near or long term future. It is the nature of technology.
Now, some might say that in some far off future where all sorts of sci-fi type plasma, ionic, and powerful force fields are possible to protect a vessel, that must be created by the huge power sources only available on large vessels, that this may end. But I say to that...not so fast. Yes, it may take the large power sources only available on such large vessels to create the shields, but that does not necessarily mean that a weapon, that can break through the shield cannot be launched from a vessel that does not have that size. With nuclear weapons or, one day, more exotic weapons like anti-matter weapons, gravitonic weapons, or even space warping or bending weapons that create temporary black holes, singularities, or other quantum events, there will still be the possibility that a weapon can be launched that could defeat the capitol vessel. So,smaller vessels will still be needed to ride shotgun, protect and defend the larger vessels.
Anyhow, that's how I see it.
