The ''is left'' form is more suitable with a reference context, for instance where the speaker is narrating something about the future. Such forms fit mostly in prose and fiction. On the other hand, the ''was left'' form most appropriately finds its use in dialogues. I'm the one that downvoted you.

Is left or has left?

He is left is incorrect. He has left is correct. Both he is gone and he has gone are correct. The verb go has a history of irregularity that just needs to be accepted without rules.

What is past tense for left?

The past tense of leave is left. The third-person singular simple present indicative form of leave is leaves. The present participle of leave is leaving. The past participle of leave is left. Find more words!