I am very sorry that your son has started to have seizures! They can be difficult to get under control but it does take time. You need to find the right medication, right dose and right timing of the doses that helps your child without too much sedation. It can take 4-6 weeks to really figure out if a med is going to do ok and for some of the side effects to ease up.
Diastat really is great to stop the long seizures, but it will sedate him for awhile afterwards. He needs that rest after one anyway.
Most children with epilepsy do not have cognitive issues. Around 30-40% will have some issues with learning, though. There is testing available to see if the seizures or medications are affecting your son and what accomodations he might need.
It is very rare for a child to die from his seizures, often it is a child on multiple medications (3 or more) or one who has other health issues as well. It is so scary to deal with seizures and live with the fear of all that can happen. Reading the safety advise can really help you make a safer home for him. Safety pillows, using a monitor to hear him as he sleeps, supervision on playgrounds and in the bath can all reduce risks. It is tragic that some children have died because of epilepsy.
It is a good thing to get that second opinion and feel secure that you are doing all you should be doing.
Sounds like you are on the right path. I know it is very overwhelming at first.
You can get some very good basic seizure information and first aid at
www.Efa.Org go to answerplace. They will also send you some free information.
Www.Epilepsy.Com go to the left hand menu and you can find a lot of very good information on seizures, treatment and learning issues.
I wish you and your boy all the best.
My son has been having seizures since he was young, but was not diagnosed until he was 7, he is now 14.