"Gone" is the past participle of the verb "go", it is also an
adjective.
The adjective "gone" has a couple of meanings. I can't list all of them here, so it will be great if you can look up from the dictionary yourself.
Some of the meanings are: dead, pregnant, ended, past, missing, used up... etc
So, does "I am gone" sound grammatically correct to you now? If "gone" is an adjective, "be gone" is surely correct.