The runners are sending out new roots. Remove the dead crown, leave the runners and fertilize next spring (and every spring) during the growing season with an all purpose fertilizer.

How often were you watering? Is the soil moist or dry when you insert your finger?

Keep the soil moist (finger test, surface water as needed), and this will promote root growth.

I just planted some more of these yesterday to fill in some open soil areas along my flagstone walkway.

I fertilize at planting time with a deep watering to help the roots establish, then I surface water daily (as needed) until new growth appears - always checking soil moisture level first (learned the hard way) - finger test the soil - if dry, water, if wet, leave it be, if moist a light surface watering will suffice.