Two outcomes: Either they'll try to make it as bad as possible for Britain in order to scare any other countries away from having elections about whether to stay or leave ( Quite a number would probably leave if their population actually got a chance to vote)
Or they'll try to Ease Britain out in order not to make waves.
If Marie Le Pen wins in France, they'll be next to go, Greece will be following and so on. A survey in Germany showed that 60% of the Germans were tired as hell of paying welfare to all the mediterranen states, because they thougt it was more fun to lie in the sun and drink wine than work, and more or less bancrupted themselves ( Government corruption played a large part, but sheer lazyness and stupidity did the most).
Also the " Wir shaffen es" thinking about being swarmed by the half of Africa and the whole of Syria, with a fair lump of Afghanistan tossed into the mix, has faded, so I believe that once the snow ball starts rolling, Germany would quit, too.
Then we would follow.
The end of " United stated of America".
Hope to be around to witness it.