Looking at how our midfield has been affected when hit by injuries or suspensions I think we'd miss Flecky more. But then again we desperately missed Leon when he was out! Good question.....
If we lost either through injury, rather than selling and replacing, i think answer would be Fleck! Only Adam Barton can play that role and we all know he doesn't have it in him to do it with as much consistency as Flecky. Without Leon in the side SP would rely on Fleck to implement a new style of play, so maybe that is the answer.
But who would be harder to replace after a sale?........Flecky again for me!