Despite the catch by Rice (who also burned Jenkins twice by the way), Sensabaugh excelled in man coverage ... and that's one of the reasons Dallas got him, to play that role.
I have no doubt he would do well playing as the deep man, but then we would be back to the same kind of situation we had with Roy Williams ... teams would be looking to get our strong safety in one-on-one coverage (if it's Mike Hamlin), or would be looking to run over Ball. I do believe Ball could handle the SS position (as Dallas is currently using it) better than Hamlin because of his matchup cover skills, but Sensabaugh is better suited for the position.
You need a strong run supporter and good man coverage player at strong safety in this system, and a good zone coverage man at free safety. Putting Sensabaugh at FS simply weakens the SS spot.