Other than "don't take those missions" and "run towards one another quick," are there any general strategies for dealing with deploying scattered?
If you're scattered into 3 teams that you can set-up yourself - make sure to balance them out properly. It's also a good idea to keep all your teams decently close to each other so that they may support themselves if bumrushed by a regrouped enemy.
If you're scattered completely randomly, but the enemy can deploy - just avoid like the plague tbh, I don't think there's any way of doing this other than "run towards one another quick" because you're always at a disadvantage here.
If you're scattered randomly, but so is the enemy - sit back and enjoy the show, if you have the guts. I had some of the most hilarious skirmishes from these starts because they are so very unpredictable and forcing you to adapt on the spot.