Snowden’s charges had a maximum of 10 years. If he had surrendered and pled, he would be free in America soon. Instead he gets to spend the rest of his life in Russia. That was his choice.
Each year in prison shortens your life expectancy by two years. So he'd be out soon, but very very unhealthy. Better to be in Russia. It's not the worst.
He could have been free - or he could have suffered a 'mishap' in prison. Not that things have ultimately worked out well for him, but I'd understood Russia was merely a stop-over from which he realised there wasn't going to ever be a safe onward option, so he's stuck.