1. They will sue. Medium to large - in fact any mature business, considers lawyers and the threat of lawsuits and litigation as a cost of doing business. They don't get emotionally involved, they just do it. FYI, looking at lawyers & legal as cost of doing biz is a healthy attitude and may save you a heart attack.
2. Telling someone to just "fucking sue me" or simply "sue me" makes it combative and I made this beginner mistake early on in being a CEO. I actually simply asked their lawyer if he thought his case "actually has any merit?" in a cocky tone in a phone call. Turns out he thought it did. Once I had capable council on my side she had to work hard to make nice with the other side and bring it to settlement hours before we were irrevocably committed to litigating the issue.
Lets put it this way: Wouldn't it be awesome if everyone you signed an agreement with "just signed it"?