Stranded pop from ground invasion after empire elimination

The 1.0.36 update listed a bugfix in which "the game is no longer stuck when an empire is eliminated while performing a ground invasion."

This got me thinking - if an empire is eliminated while a ground invasion is in progress elsewhere, what would happen to the military forces stranded on the planet after their empire fell?  Would they all continue to fight to the death, or would they surrender?

I propose that given the right match of empire personalities - invaders that aren't inclined to fight to the death, and an invaded empire that isn't inclined to hunt a people down to extinction - a ground invasion in progress when an empire falls would result in a population point of refugees being created on the planet.

This would be a rare occurrence (given the unusual circumstances) with a unique notification, and a happiness debuff on the planet hosting the stranded population point (as not everyone might be happy to host former invaders, and the stranded population might resent their situation), with this debuff varying up and down over time and eventually declining as the war recedes into history.  Random events could occur that are connected to the population, giving a story to their long process of integrating or leaving the empire to live elsewhere, depending on what choices the player makes.

If we wanted to make this phenomenon less rare, failed ground invasions could occasionally lead to a portion of the invading forces being captured as war prisoners, and players being given the option to repatriate them to their empires (for diplomatic bonuses) or to rehabilitate and integrate them (for the additional pop point).  Events like these would make wars resemble messier clashes that leave lasting, often unpredictable cultural effects.