Can you post a photo? Your description is not very clear about how this plant is growing and what's alive or not. A photo would help clarify that and give us better info to answer your question.

Unlike Swamp Milkweed or Tropical Milkweek that has fiberous roots, the root system for Common Milkweed is a rhizome. It looks like a horizontal branch. That's how it spreads. Dig far away from the plant but not very deep, or you won't see any other nodes or roots.

Interesting, never k ew that. Thank you Ceci.