Captain Jack and River Song need an adventure together. Period.
Of the "old" companions, Martha is really the only one that has any reason to show up again, assuming she still works for UNIT.
That said, Tennant's "final tour" in the The End of Time pretty much gave us closure for all of his companions. There's no necessary reason to re-open their stories.
Just going back to this post - it's interesting how companions now have 'closure', back in the day, many just disappeared in a couple of cases just blown out into space to die and be forgotten or left on a sofa!