Sooo in terms of order, the sabo first turns the opponent's sub around (your agent), then the agent swaps the owners of both subs and destroys the drillers.
So if the whole combat plays out, you get exactly what you saw.
The sabo's description doesn't say it ends combat, so I would assume the double agent's ability still applies (for all you MtG fans out there, the sabo's ability goes on the stack, then the agent's)
It's a weird interaction though. Thanks for pointing it out!
"Can I make a suggestion that doesn't involve violence, or is this the wrong crowd for that?" -Hoban 'Wash' Washburn, Serenity