He was banned for the Confederate flag on the license plate, unfortunately it's considered "offensive" and "racist" in the United States currently. You can export ROBLOX "models" if you can still export a level as an .obj file, but it's not worth it in the long run. If you start from scratch in Blender you will end up with a far better, far cleaner, and higher quality end result. For example, since I have a 3D model and a ROBLOX build of the same car; (SCREENSHOTS ARE OLD, I quit ROBLOX back in June 2017.) Early C3 Corvette, 1968 or so. Note how much smoother the model I made in Blender is vs the one I built in ROBLOX. I would have to do about as much work to clean the ROBLOX build up to make it usable as I would if I were to simply model it from scratch in Blender.
