upadkiem

In a sentence

• Poślizgnął się na lodzie, co zakończyło się upadkiem.

  He slipped on the ice, resulting in a fall.

  Here 'upadkiem' is used as a noun in its instrumental case, signifying a specific 'fall' from the action described.

• Opowieść kończy się dramatycznym upadkiem bohatera.

  The story ends with the protagonist's dramatic downfall.

  In this instance, 'upadkiem' metaphorically refers to the protagonist's 'downfall' or decline, again in the instrumental case to describe the manner in which the end occurred.

• Musimy znaleźć sposób na poradzenie sobie z upadkiem firmy.

  We must find a way to deal with the company's collapse.

  Here, 'upadkiem' represents an abstract concept, the 'collapse' or failure of a company, applying the instrumental case to indicate the context of the problem.