> So if Alexa is a colossal failure and is going to lose $10B next year, does that mean all my voice-controlled thingamabobs are gonna stop working

yes. whereas if it's a resounding success... well, same thing. this is the unavoidable fate of every remotely-controlled device you've ever thought you bought. they have to pull the plug on the old models so that you buy the new ones! after all, these services don't pay for themselves, right?
wrong, you guessed it. the services do pay for themselves, as they sell the data they collect from you through the devices, but who'd have thought that would ever be enough to motivate them to keep the servers running, when they have the power to unilaterally brick the stuff you paid for?
freedom-respecting devices, programs and services are the only way to avoid this kind of trap. fool yourself believing it doesn't have to be that way at your own peril.