in real life if 2 planes collide both planes go down
In the 'real world', you both play on the same frotnend and there is no lag. That's why if your plane gets in contact with his plane, his plane will also get in contact with yours.
Not necessarily in Aces High.
I took my Pony and rammed another P-47. This is the moment of collision:

The message I got on my screen (not visible in the film viewer) "You have collided".
But this is what the very same moment of collision looked like on the P-47 pilot screen:

Note the message "Lusche has collided with you." No "You have collided", because on this screen both planes are actually quite a distance apart.
So it's possible that I collide with you, but at the same time you do not collide with me. In case both planes actually collide with each other (on both frontends), both will take damage of some kind. Look at the messages you get in a collision, they tell you the whole story.