Consciousness can end temporarily, perhaps permanently. This in no way suggests that it’s an illusion.
The claim that consciousness is an illusion has always seemed like nonsense to me; for, if consciousness is an illusion, who experiences that illusion? Answer: the conscious mind.
Consciousness is a trick for human neural network to simplify some calculations about the world. It was developed as an evolutionary trait and proved useful to survive. That's my opinion. It's not an illusion, it definitely exists as an particular configuration of neurons.
The claim that consciousness is an illusion has always seemed like nonsense to me; for, if consciousness is an illusion, who experiences that illusion? Answer: the conscious mind.