Answer: In the Monrovia catalog there is no plant listed as "Windbreak Pampas Grass" so I am not certain exactly which plant you had. However, according to your zip code, you are gardening in winter hardiness zone 6B. The Cortaderia group of pampas grasses such as Cortaderia selloana are only considered hardy to zone 7, so in my experience I would think it is a case of winter hardiness being the problem. (There are many other, hardier, ornamental grasses that should do fine for you.)
Monrovia plants are sold nation wide by independent retailers. Any replacement warranty is based on the policy of each nursery or garden center. You might try asking the manager at Hicks Nursery about it, but it is strictly up to each store. I am really sorry you lost your plants.
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