Your pest controller should either have advised you on how the rats were entering or made an effort to block the access. Rats will return if the access is still available to them. I believe that sealing up holes with silicon sealant is a good way to deter them as a pest controller once told me they hate the texture of the sealant and don't tend to try to chew through it.
I would speak to the pest control firm you called out. They may charge again but maybe it's worth it for the peace of mind. Rats are one of the worst creatures to have in the house because they are prolific, very dirty, cause terrible damage and make a lot of noise.
Environmental health officers will give you advice about rats if you ask them but they won't come and do treatments in your house.
As far as health effects go, if no one is sick in the house it should be okay. The rats weren't sharing the living space with you and were in an inaccessible place, so at least they weren'r running around the kitchen or anything. Keep your eyes peeled for any evidence of rats appearing again - or mice as they might be present where rats aren't.
It's an awful feeling to think that your home's being invaded like this, but its only in recent decades that we have gotten used to living without some sort of vermin in the house.
