What happens to everything?
1) Population - stays where it was at the end
2) Buildings - stay where they were at the end
3) Ships - go various ways, depending on stuff, including random
4) Technology - does the empire to which the other surrendered get all the tech? Some?
5) Spies - do they all disappear? Why not defect in ways like the ships do? Why not, for instance, randomly nullify or place themselves on empires' improvements analagous to ships going pirate?
6) BCs - does the empire getting the surrender get the treasury? What if the losing empire was in debt? Does it get that?