Welcome!
The thread title might have read 'Willow Killed by Dish Soap'. Dishsoap destroys cuticular waxes in the leaf cuticle, leaving the leaf vulnerable to excessive water loss, disease pathogens, and insect herbivory. If the solution makes its way into the soil, it destroys root lipid membranes making water and nutrient uptake more difficult, creating a double whammy.
Insecticidal soaps are specially formulated from long chain fatty acids of potassium and much easier on foliage, but should be disallowed from getting into the soil whenever possible. Aphids can also be dislodged by a sharp stream of water from a hose, with little chance of injury to the plant.
No problem starting the new plant in the same spot the old one perished unless you suspect the soil had something to do with its demise.
Al
