It's a fair question though. Despite the "If you don't pay for it…" mantra that people like to spout off, situations like Sparrow and other paid services shutting down tend to worry me. And I know, it's odd, considering Gmail is free and Google as a tendency to shut things down (but I don't see them shutting down Gmail).
I guess the issue is that if I pay for it, I'm investing time and money into something I want to know will stick around. And because I'm a customer, I feel like I'm empowered to believe that. After all, if a company is charging me X amount, I think that charge should be related to keeping themselves in business. I hate the idea of a company that charges not being able to stay afloat because of their low prices. It's not even giving me a choice as a customer to pay more to ensure their service remains.
Basically, since they sold themselves to Opera, they're at Opera's mercy to keep running. If Opera shuttered their doors or if Opera felt like pulling a Google Reader, there goes my mail provider. I'm iffy on the future of Opera as a company, which means I'm iffy on the future of everything they own regardless of that product's history.
Then again, I don't really see the point of not using Fastmail as long as you can export your stuff.