They can always do economic sanctions. Just look at what happened to GBP after the Brexit vote.
That's related to the fact that the markets believe that the UK boarded a train loaded with nitroglicerine, going downhill with failing brakes.
Brexit is the UK imposing sanctions on itself. You can watch the GBP tick up or down according to how likely it looks to actually happen on any given day based on stupid statements by the PM.
Without outside money Switzerland would be in a much worse situation.
What? That is exactly the opposite of reality.
Its the UK that want hard Brexit.