It is indeed hard to imagine, but I find it significant that Mr Knightley's approach is different from Mr Darcy's (one word from you will silence me on this subject for ever --P+P ch58) and Captain Wentworth's (A word, a look will be enough to decide whether I enter your father's house this evening or never --Persuasion ch23). They both sound like they can't bear any further uncertainty.

Mr Knightley, by contrast, doesn't come across as quite so much of a desperado. His "... dearest you will always be, whatever the event of this hour's conversation..." (ch49) seems to leave open the possibility of later reconciliation, even if Emma turns him down, with or without mentioning Harriet as a very agreeable alternative. It also dove-tails nicely into the compromise Emma recently wished for: his remaining single all his life (ch48).