Then, how do you picture 500 planes getting returned and leasing companies instantly re-leasing them to other customers to keep their own business afloat? Even if that does happen, worst case, that will reduce Russian air traffic to something like Covid days-level. There are a lot of hypotheticals in this thread, facts on the ground right now are, the planes are flying, cargo ships are delivering and all but 7 banks are moving the money across the borders just fine.

Home-build - maybe, but not without parts from the US\EU, not to mention most of the production equipment is not Russian too and you have to maintain it or replace it at somepoint.

Oh and to build something you need materials - some are local, some will have to be replaced if possible.

This will be a huge problem, especially in a country with strong corruption tradition.

Whatever the US role in the events in Ukraine was, for sure they won't let Russia off the hook easily after this invasion.

Putin will make a law that returning airplanes to abroad is illegal. Foreigners have not been allowed to sell Russian shares already nearly a week. So nothing new there.

They cannot fly to most countries anyway, so the risk of getting them confiscated while landed somewhere is small.

Is there international treaties covering such things?

Mind, I'm from the UK our government just ignore international law when they like and only to please their own ends, not even in times of crisis, so can't see something as simple as breaking a treaty will cause any change here.