The legal implications of Brexit, like all of the implications of Brexit, seem either to be (i) total catastrophe and (ii) business as usual +/- 5% change. We can all hope for the latter, but in 40 years of policy and lawmaking, there are few areas of commercial endeavour that have not been touched by our relations with Brussels and so far there is no real clarity on what the legal implications are. The biggest implication, therefore, is uncertainty which should create opportunity for lawyers and clients alike.
If the job of an entrepreneur is to make money from solving problems, then the commercial lawyer's job is to solve the problems for the problem solvers. There will be plenty of work for everyone solving the problems that come out of Brexit which should be good news, unless the economic damage is so great that the economy disappears completely. If that happens, then the legal implications will be secondary to everything else.
In reality, there must be some economic destruction as a result of Britain's exit from the Eurozone, and there are certainly plenty of laws to re-write, but the optimist in me sees the destruction constrained to badly or structurally vulnerable businesses (Carrilion for example). For example, most financiers that I have spoken to see moving the infrastructure of a large institution as a 10 year project requiring huge time, investment and commitment. (How much commitment it takes to move from Mayfair to Luxembourg remains to be seen). In short, there are almost no fields of legal practise that will not be implicated if not impacted by Brexit. Change that doesn't kill the economy is generally stimulating, and even a heavy Brexit-lead pruning of UK business will leave space for vigorous fresh growth.
For every negative and depressing idea about Brexit, there seems to be a positive alternative. For example, European investment into the VCs who are reliant on the funding will dry up, but the pound is 30% cheaper than it was, banks in the eurozone are charging their clients to hold deposits and some institutions are lending in euros at 0.5% interest rates fixed for long periods. So there should be private money available to replace the centralised capital if it can be convinced to venture into the venture capital world.
From a legal perspective, we just don't know what the changes will be, but the indications from the government for post Brexit regulation is to make the UK more robust rather than less around the key European legal talking points of anti-money laundering, know your customer and general data protection checks. In the absence of better information, we should assume that the post Brexit regulatory environment in the UK will be intended to be business friendly, but to offer an extremely high level of security both of personal data, and a robust defence against using the UK as a destination for illicit financial activity.
As a result, and in the absence of clarity, the best thing any business can do is to keep on with its compliance preparations as they will provide the strongest point to jump off from into a new compliance regime if it comes. The worst thing to do in an environment of uncertainty, is nothing at all.