The Regal could sell better with no Verano there, but I for years have thought Buick needs a small car because no one makes a small luxury car. All the small premiums are like the Golf GTI, Mini Cooper, Volvo C30, etc that place the emphasis on sporty driving. I actually wish the Verano had less Cruze to the interior and were a bit nicer. The exposed cup holders, short armrest and shifter are more economy car than luxury car.
By T61's figures, clearly the Verano isn't taking sales from the Regal, so that answers that.
I wonder how much staying power the Regal has, the interior isn't that impressive to me, the seats and everything you touch is hard. It is pretty well made, so I don't think it is a bad interior, it just doesn't wow me in any way. The Regal has weak engines also, it is outpowered by the Sonatas and Camrys of the world so I don't see how they are making the sport sedan claim. The Regal just seems like a car that can quickly get dated and forgotten once the newness wears off.