No they don't still want to mate.. The guinea pig is like a dog, if the get fixed they wont want or have the temptations any more.
A neutered guinea pig is unable to make female pregnant but he has sexual desire and try to mate with females. His instinct to fight with males due to females is also not lost. But this can cause stress in female guinea pig. So, it is better to keep the separate when the queen is in season.