wow i am so sorry you are going thru this, i udo not think seizures cause brain damage. all these questions should definatly be asked to his doctor at the moment.
One of my twin daughter had seizure when she was 9 months old, she is now 22months and did not have any since. But I also have been very careful with her. Drs told me that it is common to have seizures and may happen again so keep an eye on fever. She had 104 when EMT took it at home, then at ER went to 98 with tylenol and motrin then released. They checked ears- clear, put in catheter no UTI. I was so scared with the situation at the time it happened. I called 911, then from cell call hubby and neighbor.
anyway, I know other kids who have had seizure only once and others with many. My sis's son has had a few already. He gets ear infections then fever leading to seizure. by the way, they say breastmilk help keep the ear infections away, well he has been just having breast milk when this happened.
It really depends on how long the seizure was happening and what happens to the child afterwards. I have read that it can lead to serious issues and and sometimes nothing. take care.