Even in the extremely unlikely event of a catastrophic failure of the entire Amazon Cloud system at once, the agent has its current information, heuristics, and manual tools at its disposal. Everything else is cached locally. When the system is back up, the cached information flows and action is taken at that time.
An interesting part is that the manual removal tools in the agent can be used with the full capability of the cleanup engine even with zero cloud access. Very few AV programs have any use or capability at all if their definitions are completely missing.