https://medium.com/@octskyward/ok-what-now-e3f64d38f7#.q4vch...
It is almost without question that the Swiss will hold another referendum in the coming months, as their deadline for implementing the previous referendum's legislation (which they are legally bound to do) will expire in February. However due to the latency on getting new laws through Parliament they really have to start now.
There is no way to renegotiate with the EU because the EU sees any geographically European population that chooses to defy the EU as some kind of terrorist, with whom negotiation is unthinkable. They refused to negotiate with the Swiss and are now demanding the Swiss join the EU proper or else there won't be any further negotiations (ever). The Swiss do not want to join the EU. So the stage is set for a showdown.
The best case outcome for the EU is a new vote in which the Swiss choose to continue the status quo for a little while longer.
From what I've seen, the answer is pretty much none. So long as barriers to tech talent aren't put in place, there's basically nothing holding back the UK tech scene. The fear being generated by the media (along with those that repeat those fears without critical examination) is more damaging than the situation as it stands today. We're talking about something that only happened within the last few weeks, the sky isn't falling, it's all a failure of perception.
Immigration restrictions are the least of worries for UK-based startups not focusing on the domestic market though, especially in fintech which has traditionally been London's strength. If you need company registrations, offices, contract and potentially even servers and compliance staff to be based in the EU to comply with certain regulations, it suddenly makes a lot less sense to spend all the extra overheads of having your [main] office in London, especially if other startups on the scene are starting to migrate and you don't want multiple offices. And whilst EU negotiators might want to avoid tariffs regardless of whether the UK stays in the Single Market or not, they have very little reason to secure trade agreements with the UK that grant UK firms passporting rights.
If you disagree I'd enjoy a thoughtful response