Yes, these are very persistent plants... they will reappear each spring no matter how tough you treat them!

I leave mine until they stop flowering. I do make some attempt to dead head but they are so prolific it is almost impossible to get all of them. I cut them to the ground and put a mulch over the crown

I leave mine until about november then cut down to about 6" so there is evidence of them before I dig them up by mistake. Mine are still in flower at the moment.

I cut right back to their base as soon as all the flowers have gone. Mulches aren't needed here....