As the survivor of three mild Dummies, I am holding mt breath here.
Brain damage in a horse is actually not that serious, they do not use their brains as much as we do.
I had to pattern my worst one, and teach him things he would normally have learned for himself, like nursing from the bag instead of the hoof, the wall, my nose etc, but once he got the hang, he was fine.
This is not "Hydrocephalus, BTW this is Dummy foal, there could well be some swelling and some water retention, but that should take care of itself if the foal lives.
Once I had my worst one sucking and following Mama, he went on to make his other milestones normally, if a little late, and by the time he was a yearling he was just a normal animal all round.
He was a red bag, slow delivery, but he was not breech...is this foal also Preemie, would be my first reaction, all mine stood almost normally, but if he is Preemie he would well not do.
If the mare were not too distressed it might be an idea to take him off and hand rear him, obviously on Mama is best, but sometimes they do not get enough milk that way.
It's obviously up to the owner....
I do hope this has a happy ending.