Not sure I would count it out in the very short term. Thinking we have a 50% chance of a Z06 convertible being announced just 34 days from now, at the opening of the Geneva Auto Show on March 6th, where, as you know, GM has been revealing its convertibles for a while now. If as Redc7 suggested, the widened Z06 rear fender area is able to handle the fender air intake grill for cooling the trans and the diff, the above picture shows how it would probably look. However, if, like the StingRay convertible, the intakes are located below, because they would similarly interfere with the top lowering and raising mechanisms, thanks to photoshopping, here is what a Z06 convertible will look like.
Can we wait just 34 more days?