I don't mind the thickness of the A-pillars at all. I am much more concerned when cars don't offer good visibility out of the rear window - like in the Model S. Will be interesting to see how the Model 3 does in this respect. A rear-view camera is certainly nice, but sometimes plain old proper visibility out of the rear window itself is handy as well.
And as for safety, I am sure the Model 3 will be one of the safest cars in its segment, so no worries there. Especially concerning the roll-over / flip over scenario, as I have never ever seen such a thing happening in a non-SUV travelling at "normal" speeds. When I saw that video earlier on about that road rage incident I immediately thought "what an idiot" about the driver of that white SUV/pickup which rolled over. I mean from the footage it was clear that he must have noticed the accident. The car swerved almost into his lane before, then crashed into the barrier, then came back towards him. But in contrast to the driver in the lane to the left of him he didn't slow down or react in any sensible way but just kept on going as if the accident was of no interest to him at all - until the other car hit him. I mean what did he expect - that the other car just disappear?