Are there any novel or sources that mention what happened after that? Or are there any other stories about Jem Hadar without addiction?
There is an article about Goran'Agar on Memory Beta, which sheds some light on his fate.
According to the Avatar novel series (Book Two), the Vorta did a search for other such "deviants". The search took weeks, and turned up a total of four Jem'Hadar capable of surviving without ketracel white, including Taran'Atar.
He never again appeared on a Star Trek show (as of the end of Enterprise), nor have there been any movies featuring Jem Hadar.
Thus, in canon, he's not been heard from again.
The 'extended universe' of Star Trek, unlike Star Wars, is non-canon, so if he's been featured in any novels it's still not 'official'.
That said, I've not read any ST novels which feature Goran'Agar or any other 'free' Jem Hadar.
Aha I found one. It is Taran'Atar. He is an honored elder Jem Hadar from the book "Warpath". He is chosen by Odo to familiarize Jem hadar with other Alpha Quadrant species. He is chosen because of his lack of dependency to ketracel white.