Will Krishna appear on earth again?
Krishna Himself says in the Bhagavad-gita that He appears on earth whenever and wherever there's a decline in religious principles and a rise of irreligion. It may seem to us that this is already happening, and we may wonder why He isn't appearing all the time.
This question was also asked at a gathering of sages just after Krishna's departure from the world, around five thousand years ago. This was recounted in the Srimad-Bhagavatam, 1.3.43. The answer is that Krishna exists as the Srimad-Bhagavatam, which tells of His many incarnations and His relationships with His devotees. So, the Srimad Bhagavatam is considered an incarnation of the Lord.
Furthermore, Krishna also appears in His name, specifically as the Hare Krishna mantra, so that in these troubled times, Kali Yuga just by chanting the holy name of God anyone can come to know Krishna. The next scheduled incarnation of Krishna is the Kalki avatar, Who is scheduled to appear in 427,000 years.
I hope this is helpful.