Why Villeneuve would not wait out Nelson at Cadiz

Could Villeneuve have stayed in port and waited for Nelson to retreat?

Nelson was not going to retreat, while the impending arrival of Villeneuve's replacement gave him a personal reason to seek battle.

Villeneuve's departure is explained through the approach of Rosily, who was coming south to replace him. Fighting offered a chance to recover his honour and reputation before losing command. The expectation that Nelson would simply withdraw to Gibraltar offered no dependable alternative.