It seems like a pretty reasonable concern to me. We can presume the odds are pretty low, yeah. But the consequences are very high - you would need to redesign and possibly rewrite in another language your entire application. People complained up a storm about Reader dying, but it was a 5min process to export your subscriptions and import into another web reader that had basically the same feature set. Conventional Linux hosting, or even Docker, could be pretty easily re-hosted as-is on any of hundreds of other places.