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Try to tug at the roots, do they loose in the ground?
If they roots have died, you can pull out clumps of the plant.

Peek down into the grass to see if you see any signs of life.

Give them more time; grasses can be the last to make an appearance in the spring.

https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm

Pick a well-draining container for your grass. The pot should be at least 18 inches in diameter.
Fill one-third of the pot with a mixture of potting soil and compost. The ratio should be 50/50.
Place the root ball in the pot. Fill the pot to the rim with the potting soil and compost mixture. The root ball should be completely covered and not protrude from the top of the pot.
Water the grass thoroughly until you see water streaming from the bottom of the pot. Water the plant weekly in the absence of less than 1 inch of natural weekly precipitation.
Fertilize the grass when you first plant it. An all-purpose 10-10-10 fertilizer is ideal.

It's possible you may need to stake the grass while it is getting started.

Have you cut this down already for the new growth to come up? You should wait to trim these until they start to grow green here and there. Pruning them early in the fall instead of spring can cause the plant to die prematurely due to cold weather, and the crown being exposed to it. This article will help on the care of this grass: https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm

Late winter is the best time to cut back your Pampas Grass.
https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/pruning-pampas-grass.htm

You are in planting zone 6a and the planting zones for pampas grass are 7 to 11. So it is possible it just froze out during the winter. Also, you may have experienced a dry winter, and without supplemental watering, you can lose plants.

Here is general care for pampas grass, you might see another reason it didn't come back:
https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm

Usually, this kind of damage will not affect the grass much, however, cutting back at this time will. It is best to leave them damaged and cut them in early spring, as they use the dead tops as insulation from the winter.

If you don't see any growth by next spring, then it is likely that the untimely pruning will have caused the premature death of the grass.

This article will help you with the care of Pampas Grass: https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm