I think in that case, the expectation is that you (as a founder) have no obligation to "keep a place in line" for them. If they never responded, you can consider it a "no."
When is the investor considered to have "stepped out of line"? an hour, a few days, a week or more? What happens if the investor doesn't reply, the startup assumes the no reply is a no, and weeks later the investor sends an out of context "yes" hoping to cash in on the terms of the earlier deal?
I know this sounds like a petty concern for a "handshake deal" but the startup's e-mail at step 3 creates a paper trail that an unscrupulous investor could abuse.
