It also depends on how important Earth is to the Federation and just how much of its starship development and engineers are on Earth at that time. As well as how many people of the people being "removed" would harm the Federation on an economic level as well as just on the level of workers for the various shipyards and such in the Sol System.
It seems there were no other major ships in Sol at the time. Or at least none in a condition to intercept V'Ger. So the current Starfleet is intact in terms of ships and non-Earth bases. But how about the command structure, both Starfleet Command and the Federation Council?
Just how important is Earth to the Federation? What does losing all the people on Earth in 2273 do to the Federation?
This could have a similar question for the newer films with the loss of Vulcan, in what does that do to the Federation? The loss of billions of Vulcans and the whole planet.
At least with Earth, it is possible V'Ger leaves all the technology and ecosystem in place...just removed the humans, gets disappointed and is destroyed by a self-destructing USS Enterprise. The wreckage probably will do a number on Earth, though.
Good points!
I hadn't remembered that there were few/no ships near Earth when Enterprise launched. Where the heck were all those other ships? Anywhoo... you're right in that Starfleet, at least the physical fleet, would be short one ship but otherwise unaffected.
Now with the loss of Vulcan in ST09, I think that should slow down advances in technology, since those vast learning centers are gone. Of course, Marcus compensates for this in STID by bringing back Khan and building Vengeance, so YMMV.