Symbian was going nowhere and the leadership at Nokia failed to move on to Android or something else. I think Nokia would have been in a much worse position had they waited and kept going in the direction they were headed. Symbian smartphones and feature phones would have been losing sales just the same as they have been with or without Lumia line, albeit at a slower rate.
If Nokia had gone with Android instead they would have had to ramp up sales just like Lumia WP line. You can't just walk in an established market with a dominant players and grab huge market share instantaneously with no marketing cost. That is ridiculous to assume. They would have to go against established phones and marketing from Samsung, Motorola, HTC, Sony, Hauwei, ZTE etc, etc, etc, competing on only price and build quality.
With Lumia they can compete with price, build quality, different user experience, Windows Branding and free marketing from MSFT and ATT. Sounds like a no brainer to me. Not to mention a billion dollars from MSFT. Given the choices, what decision would you have made.
1. Stick with Symbian
2. Go with Android
3. Go with Windows Phone
4. Some other platform
I'd love to hear your response, but I'm pretty certain it will be unintelligible