Is the owner still willing to sell it to you?

If the the purchase agreement has not been signed by both sides, nothing is garanteed. And I doubt whether the owner will be still willing to sell it to you, after this event, the closing process wouldn't be pleasant to him -- If I were him, I wouldn't move on with you, just not worth of it. By the end of day, it's the market gives the final say, and if your offer is not particularly good, he can always keep looking.

After that kind of conversation, the decent owner absolutely just hold it off, and wait for any possible legal action you may want -- and the only thing unwanted should be your purchase.