Does the synthesis tool take care of the properties of casex like even if the case items are unknown it will be able to produce the valid outputs against the case items? If the answer of the above question is true , in that case synthesis tool will have to try to synthesize a gate level netlist that even with 'x' as input will be able to produce either a '0' or '1' in your second question. I need to understand the answer of the above question to underatand what you want to say.