Breaking Face Boundaries
The screenshot shows the dialog of QBreak. After sewing the face boundaries there may remain face overlapping face boundaries or t-pieces. You have to run QBreak to break these face boundaries and then QMerge again to sew the new pieces.

Both jobs that are done by QMerge and QBreak are dumb jobs, but nevertheless they are quite time consuming.

The geometry shown in the screenshot already show the result after QBreak and QMerge. Besides the outer boundary there are still some remaining curves, which are marked by a red circle.