Simply put? If you quit colgan, be prepared to pay...
They may or may not try to enforce the contract. However it's important to know that regardless of whether they do or not, it's a written contract, that very well could be legally enforceable.
I'm seeing more and more employers these days that instead of suing the former employee, they are simply selling off the debt of the contract to a collection agency. While they don't recoup all of the money on the deal, they get a good chunk of it, and the collection agency then can utilize their large resources to claim the rest of the contract (often with interest after they win a civil court suit).