Anyone may stop or start worshiping any number of gods or goddesses at any time.
Neffertiti
Nothing would happen. l don't think anyone believes in greek gods anymore.
In Buddhism gods and heavens are mentioned. But it is not about worshiping gods
King Solomon broke the commandments against worshiping false gods and having many wives. He allowed his many wives to lead him astray into worshiping their foreign gods, which angered the Lord.
They were polytheistic, meaning worshiping many gods and goddesses.
Worshiping Nyx is not considered Witchcraft alone. You are simply worshiping Nyx. If you wish to practice witchcraft research it before aligning yourself with any deities (i.e. Gods/Goddesses). Witchcraft is not particularly a religion and therefore the worship of Gods and Goddesses is not a rule/must, but many Witches do honor their deities.
Judaism is a monotheistic religion, believing in and worshiping only one God.
worshiping other "gods"
Achilles beliefs were of the Greek gods
The main religion worshiping Greek Gods is called Hellenic. Though many New Age Pagans also worship them.
when they became Muslim, back in the 6th century
worshiping other gods