Is there any proverb or idiom that conveys "the world is bound to no man"?

The only common usage I know of is time makes fools of us all

Time makes fools of us all. Our only comfort is that greater shall come after us.

Essentially, it's saying, with enough time passed, we'll all seem like ignorant apes, clueless and stupid. Nothing stays the same.

This looks like two questions to me. If you're looking for the English version of the Persian story/proverb, this is a good fit:

look on my works ye mighty and despair

This is a sarcastic reference to the poem Ozymandias by Percy Bysshe Shelley. In the poem, there's a worn away statue in the middle of nowhere with an inscription that boasts of the immortal empire of the man it depicts, King Ozymandias. The full text is in the link; it's short and a good read. This poem is slightly obscure, so there's a chance that a person might not get the reference.

If you're interested in an idiom with which everyone is familiar, this is your answer:

You can't take it with you

Definition from using English.com:

Enjoy life, enjoy what you have and don't worry about not having a lot, especially money...because once you're dead, 'you can't take it with you.' For some, it means to use up all you have before you die because it's no use to you afterwards.

That's not exactly an authoritative source, but the saying is incredibly common, so you can verify its meaning easily.

Well, I very much like your phrase

The world is bound to no man.

It's short, and incisive and makes you think. It also goes well with John Donne's "No man is an island."

Hamlet's

Imperious Caesar, dead and turned to clay,

Might stop a hole to keep the wind away.

also carries a similar idea. As does Shelley's Ozymandias

These last two deal with the transitory nature of earthly power. But for everyday use, bearing in mind that nothing lasts forever and Dust thou art and unto dust thou shalt return, a common phrase is:

Ashes to ashes

Which is from the Anglican burial service.

On the mortality theme of your example "the six feet of earth make all men equal," here is a line from Thomas Gray's "Elegy Written in a Country Churchyard" (1751) that has become proverbial:

The paths of glory lead but to the grave.

The complete stanza reads:

The boast of heraldry, the pomp of pow'r,

And all that beauty, all that wealth e'er gave,

Awaits alike th' inevitable hour:

The paths of glory lead but to the grave.

(ll. 33-36)