Personally, I don't think his snoring poses any danger to him. Read this article http://www.entnet.org/HealthInformation/snoring.cfm
However, why don't you check with his doctor and this will give you peace of mind. While you are checking, ask his doctor about the fluid build up and your fears. Peace of mind is very important for the caregiver and your concerns are very normal. All caregiveres feel very responsible for their loved one and when something happens it is easy to think the worst.
Is your dad's doctor "approachable" and friendly?
This is a good article on pleural effusion: http://my.clevelandclinic.org/disorders/pleural_effusion/ts_
When you read it, remember not to fear the worst but understand it for the best.
I had my lungs drained twice. It certainly is not pleasant, but was necessary. I was certainly fortunate I did not need to have it done again.
If he is sitting up, walking some and getting some exercise, the fluid should continue to be absorbed by the body. If it seems to be building up again and he has difficulty breathing, then the doctors may need to do something. As long as he is doing as well as he is, try to give him time to heal. It is a very slow recovery for some people. It took me 8 months to recover. Some people recover quicker. Always consult the doctors when you suspect something unusual is happening. It is worth a phone call.