Most,if not all assets connected to Russia have been siezed by governments all over the planet.
Removed them from swift and banned their exports in mass.
Do you really think that they give a damn about this default?
They have China, India, and Iran for import/ export and moving funding.

The rest of the world cut them off, why would they pay up?

Consider all debt Russia owed to the west as null and void.
War does that to creditors whom call you the enemy and tries to shut you down...