As well as the fact that not all of the ships in the final battle were destroyed:

Only at the very periphery of the simulator did the M.D. field weaken. Two or three enemy ships were drifting away. Ender's own starships did not explode. But where the vast enemy fleet had been, and the planet they protected, there was nothing meaningful.

These ships at the Bugger's homeworld were not the same ships used in the other battles leading up to the final one. I will try and find the relevant quotes later, but basically, there's a point made that the ships Ender has access to as the invasion progresses are older, less well-armed, and have fewer fighters - since the ships furthest away would have been sent before the ones fighting battles nearer to Earth.

A lot of the earlier battles saw survivors - who were then used to populate the worlds they'd conquered.

As to whether any of the individuals in the fleet came home after the Third Invasion: I don't think Card has mentioned it - one thing is true, it took years of non-relative time to get from Earth to the colony where Ender settled (Ender is much younger than Peter when they talk over the ansible) - by the time any of the invasion crews returned, their families and friends would be dust.

As well as the fact that not all of the ships in the final battle were destroyed:

Only at the very periphery of the simulator did the M.D. field weaken. Two or three enemy ships were drifting away. Ender's own starships did not explode. But where the vast enemy fleet had been, and the planet they protected, there was nothing meaningful.

These ships at the Bugger's homeworld were not the same ships used in the other battles leading up to the final one. I will try and find the relevant quotes later, but basically, there's a point made that the ships Ender has access to as the invasion progresses are older, less well-armed, and have fewer fighters - since the ships furthest away would have been sent before the ones fighting battles nearer to Earth.

A lot of the earlier battles saw survivors - who were then used to populate the worlds they'd conquered.

As to whether any of the individuals in the fleet came home after the Third Invasion: I don't think Card has mentioned it - one thing is true, it took years of non-relativistic time to get from Earth to the colony where Ender settled (Ender is much younger than Peter when they talk over the ansible) - by the time any of the invasion crews returned, their families and friends would be dust.