I think Android is more like Symbian than like Windows on the desktop (the analogy that Google likes to make).
Like Symbian, Android is clunky, open source, and most people buy it either because it's cheap, or because they're propellerheads.
The propellerhead contingent is loud, but small. They couldn't save Symbian or make MeeGo viable.
I could totally see a situation where Android becomes toxic due to its serious usability issues or persistent, massive and unstoppable malware infections (malware is now the largest single category of app for Android). If it gets bad enough, and Google continues its tepid response, all it would take is a nasty infection where several hundred people have their bank and investment accounts cleaned out by Russian hackers to kill Android.
There's also the security angle of BYOD. CarrierIQ on Android showed that third parties could easily hack into and collect confidential data -- whether they were carriers who used the software, or hackers who exploited back doors. If you operated the IT department at a secretive bank, or high-tech firm, would you want your people using Android devices, when said devices could easily be hacked to allow unlimited access to your internal network and all e-mail, design documents, and other incredibly confidential data?
Probably not.
All it would take to kill Android would be a massive malware epidemic followed up by corporate bans on BYOD Androids, and WP and BlackBerry 10 would take off almost immediately. iOS would also get a big shot in the arm.
Android is like that putrid "all you can eat" place where lunch costs $5, but you don't get to complain about the disgusting food (or the e-coli infection you suffer afterwards).