Yeah, obviously you don't acquire him if you don't like what you see in his medicals. A healthy lee is probably something like 4 WAR next year and 3.5 in 2016 though. IMO most every system will have Buehrle at around 2 next year. He's been there the last two years, and would be there again if not for a low HR/FB artificially deflating his FIP.
I actually really like Mark Buehrle, and have no issues paying him what he'll earn, but if given the choice between him and Lee, I'll take Lee every time if his medicals check out.