But here's the issue: Fastmail themselves may have been able to keep running indefinitely, but they're not Fastmail anymore. They're Fastmail from Opera. If Opera shuts down, what's the guarantee that they will let their purchases keep running?

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.