I think there needs to be an explicit timer between step 3 and 4. Something on the scale of a few hours or at most a few days.
-- Anderson's Business Law, Formation of Contracts: Offer and Acceptance: Lapse of Time
That being said, it appears the intention of the protocol is not to recommend a set of best practices for forming legal agreements, but rather to establish some community norms. I think the assumption is that anyone who violates the community norms will suffer a loss of reputation.
In that light, the analysis becomes easier. If step 3 happens and the investor subsequently goes quiet--failing to deliver a "yes" or "no"--then the investor has violated the community norms. (Even a "no" might be considered poor form following the oral deal, but it's certainly better than ambiguous silence.) Presumably, some community self-policing happens at this point, and if the investor remains obstinate, then word spreads and the investor is shut out of future deals.