I think Sharapova would probably overpower Clijsters. Maria has shown she has the power to slug it out with a Serena Williams with regularity, which would have been something of a stretch to say for Clijsters, who played that same style. Her ability to play it with such consistency(apart from her nervous breakdowns)is what give her a fighting chance under the right circumstances. Ok true Serena was more dominating and imposing then than now to be sure, but my view still stands.
I think Clijsters had a nice window of opportunity where she played some great tennis, circumstancs in many cases fell her way, facing Serena on an off day in the Aussie semis, facing an injured Venus in the Wimbledon semis, facing a depleted Henin in the U.S open final, facing a Henin feeling the pressure of now being the dominant #1 in the Aussie final, she failed to convert any of those. I somewhat doubt what she can do without such vacant gaps, when she had a buffet of them which she puked away in a stretch of a year. Womens tennis may not have the dominant figure that Venus, Serena, and to an extent Henin, all had periods of being, but it has even more contenders now than before, all who probably will believe they can beat Clijsters after her layoff to be sure. As I said regarding Venus as well tennis is alot about momentum. Just as Venus lost alot with the layoff and opponents establishing new positions, the same will be true in Clijsters return.