While Facebook and MySpace are different in many ways, the average lifespan of a S&P 500 company is below 20 years.

Facebook could very well be an outlier. If it isn't, it could definitely go away in the coming years.

In any case, that shows that its revenue/income is not a predictor of anything. When a company spirals down, it does so at an accelerating rate and can quickly burn through any amount of cash.