In the Forgotten Realms setting, there is an Overgod, Lord Ao. (see also this question)
He was credited as the creator of the cosmos, and even existed beyond concepts such as alignment and divine rank.
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Ao had the power to create gods out from thin air.
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...unlike the gods under him, Ao did not need the worship of mortals and did not desire it either, whereas those "normal" gods who did not receive the worship of mortals could die from lack of it.
So in answer to your question, there are Overgods who do not need worshipers.
