The law tara construction can combine two distinct effects: bringing a future scene to imaginative presence and omitting the consequence so that the hearer supplies its magnitude. They reinforce each other but should not be conflated.
The past-form wuqifu can present the event as firmly realized, while the imperfect tara vivifies the act of seeing. The unsaid response lets the audience imagine the terrifying consequence.
Reducing this to a simple if–then grammar exercise would lose the interaction of temporal framing, visual evocation and deliberate omission.