His continued reliance on Russia gives them more than enough power to force his hand into something he may not otherwise do.

what might he do? write another book? he doesn't have any power besides moral authority and he cannot travel internationally

how does giving asylum to a defector from an adversary make russia look tolerant? don't you think the US would happily do the same thing if the tables were turned?

The US routinely does the same, and they generally receive some amount of praise from the population as a result. The same thing would happen in Russia.

At this point is there a compelling heuristic we can use to determine if Snowden is an idealistic whistleblower or simply a Russian intelligence asset? The facts seem to support both interpretations.

The facts absolutely do not support either interpretation. The only reason Snowden is in Russia is that the US canceled his passport.

They revoked his passport because he's a fugitive, formally charged with two counts of violating the Espionage Act. I think the reason he's Russia is that they don't have an extradition treaty with the United States.

he was stuck in the moscow airport (for over a month) after his passport was cancelled en route to equador and was eventually granted asylum

This sounds like some sort of nutty conspiracy theory.