* H1 operating profit down 31 percent (Updates with CEO and analyst comments): LONDON (Reuters) - IWG (IWG.L) has abandoned takeover talks with its three remaining suitors in a move that ends months of uncertainty about the future of the London-listed provider of serviced offices but sent its shares tumbling. The FTSE 250 company said on Monday that it had dropped its negotiations with rivals Starwood Capital, TDR Capital and Terra Firma because it did not believe any of them could deliver a deal at a price that IWG could recommend to its shareholders.