When losing an engine, gaining speed quickly is essential. Apart from what previous users have mentioned, if you're still too heavy to stay in the air with one engine, press PAGE UP to make the engine(s) enter EMERGENCY POWER instead of the usual AUTO setting.
On my stream, in the Aggression of Georgia clip (check Highlights), I get one of my engines shot out and emergency land and take off making it back to base with the one engine left running. I think it's about an hour into the mission. I would've found it myself, but my internet right now is too slow for me to do it :)