That's where Clippy might fail at viability-- unless it's the only maximizer around, that "kill everyone" strategy might catch the notice of entities capable of stopping it-- entities that wouldn't move against a friendlier AI.

Intended to be a illustration of how Clippy can do completely obvious things that don't happen to be stupid, not a coded obligation. Clippy will of course do whatever is necessary to gain more paper-clips. In the (unlikely) event that Clippy finds himself in a situation in which cooperation is a better maximisation strategy than simply outfooming then he will obviously cooperate.