There will only be panic re negotiations if the same muppets are negotiating, reality is we need to just pause as we hold all the cards. Germany have already said that a free trade with uk if we leave is still possible.
Several other nations within Europe are already in thin ice with staying in Europe so they may vote to leave, in which case we would then be a majority.
Remember Germany and France as largest contributors have now to find an additional £20bn between them to keep the EU as it is.