Can a comet, periodically returning to the Sun, exist forever?

No, since evaporating, the core decreases and if it is a mixture of dust and ice, then it will evaporate completely, and if the core is stone, then an asteroid will remain in orbit.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.