A Sigil Portal Riddle

I'm adding material to Vecna: Eve of Ruin so the players take a more active role in Sigil. Because of this I need to add a portal they can find to take them back to their material plane. Previously, they have explored a Yuan-ti ruin in the jungle of their home plane and I locked into this as a backstory and destination for the portal.

I'd be interested if people think the riddle for this portal key seems solvable. My players are pretty smart and often solve puzzles written for the general public before I even finish reading them. 

Here's what I've got:

​At the terminus of a soot-stained cul-de-sac in the Lower Ward stands a freestanding marble arch. Two colossal serpents—one feathered and draconic, the other smooth and serpentine—are entwined and locked in a recursive struggle, fanged mouths bared at each other

​The ground around the base is banked with drifts of ancient, brittle refuse. What might have once been storied treasures are now merely dust and rust. It is a hollow collection of items that have been utterly exhausted by the vastness of time.

​Fastened to the base of the arch by rusted bolts is a weathered bronze placard, its surface pitted by acidic smog. The bronze is dark with age, the draconic letters etched in a sharp, archaic hand. As you clear away the grime, the text reveals itself:

"​Give up Ashen glories, past,

In yer Token, lost at last.

Victor Riven, tribute thrust,

Ev’ry Off’rin', now is dust.

​All your Proffer'd hopes will fail,

Worldly Honors, hollow tale.

As yer Yielded, a-ward binds,

Yonder world yawns, gate-hinge grinds."