I don't think you need to be particularly cynical to assume that Russia might eventually send him away without calling it an extradition. After all, it doesn't look like Russia is interested in actively protecting Snowden. And if he doesn't get asylum in Russia neither somewhere else, it's plausible that the "default" alternative is deportation.

Russia has done spy exchanges. Snowden "is" a spy. When it's to Russia's advantage, they won't hesitate to implement an exchange.

I don't know anything about spy exchanges, but based on the term I would imagine it works the other way: an American spy captured in Russsia would be traded for a Russian spy captured in the US. Do they usually trade defectors too?

To put it more generally, it would be for an American spy in Russia for any reason and under their control, for any similar Russian spy in America. Doesn't matter whether the "spies" want to go or not, nor how they got there. The spy exchange would be just window dressing for accomplishing some thing that either or both powers want.

Yes, defectors and enemy spies are usually the same thing. It's much more rare that they are 'inserted'.

What would have happened if it was Osama Bin Laden in Moscow airport.

Russian cops would probably shoot him. Russia probably has even more dislike for Islamic extremism than the US does. No need for extradition.

Well, to be fair, Russia does actually have to deal with them from time to time unlike the US who nearly never does.