i don´t think that a domestic market is needed to be succesful.
certainly, for us airlines their domestic is much more important to them than the respective domestic market for such carriers like CSA, LOT, SR, SN, EI, and also bigger european carriers...
but i think it depends on the airlines, the respective markets and the route structure.
cathay pacific and singapore have absolutely no domestic market and they´re quite profitable, but they have no massive short-haul network like american or european air carriers.
If only pure sweetness was offered, why's this bitter taste left in my mouth.