Surely, by the time that mining only gets you 1 satoshi in however many years that is, it will not be anywhere near viable to mine anymore. It would cost so much more in electricity to mine than what you would earn unless bitcoins price soars to the point where 1 satoshi costs hundreds of dollars. I guess that almost seem like a possibility at the moment the way the price is going but i don't think it will rise forever, it will collapse some day soon under its own weight without the needs of governments to intervene.
or ... miners turn off rigs and difficulty goes down. That combined with transaction fees should make the network viable forever. What a great solution. Too bad Satoshi didn't think of that. Oh wait he did. Difficulty goes up and down based on hashpower on the network. The network will always reach equilibrium.