So if they lost their limited liability, and got the unlimited liability like a sole trader then you could sue them personally, However, i would imagine their other halves would be the legal "owners" of their personal assets, so, what could you do, sue them for the money that you are owed + legal costs + whatever all the hassle was worth. They would have to sell up...! I doubt they would have insurance for being sued would they... Professional Indemnity right? They wouldn't have planned on being sued...!