Why should it run out?

His safety in Ecuador seems highly dependent on the attitudes of the current ruling party/president. What happens if a more US-friendly group takes hold of power?

That could happen with any country.

Since we are arguing this way - Maybe the next US president has good will towards Snowden and he will come back home as a patriot.

It would run out when they 'harbor' someone for whom the USG would have no qualms violating the Ecuadoran sovereignty to eliminate.

That would seriously harm US relations with Mercosul and other Latin American countries. The US already has a poor track record in Latin America. Invading Ecuadorian sovereignty would basically turn Latin America into yet another region with strong Anti-American attitudes like the Middle East. I'm sure Europe would also heavily condemn such an action.