Legal Question in Civil Litigation in Washington

Re: Does original (1st) contract or 2nd contract prevail when 2nd is breached?

What you are describing is the end, somehow, of an original contract, and a subsequent 'accord and satisfaction'.

However, in order for the second to prevail, it would need to be in writing. If it was an oral agreement modifying a written agreement there would be very few ways to show the existence of the second agreement.

One way is partial performance. There is also a concept called equitable estoppel which makes enforcement more likely or possible.

That said, your question as framed is almost impossible to answer. I hope this helps. Elizabeth