Geopolitically-wise, an exit by the UK would be bad. UK's always seen membership of the EU (and its predecessor, the ECSC) as a commercial entity rather than a geopolitical one.

Trade is broadly separated in the 'goods' and 'services' category. CETA and the Japan negotiation basically covers goods, and a limited portion of 'services' (Most notably missing financial services that 'passporting' provides).

Negotiation between the UK and the EU can be based on the existing . Forcing the City of London out completely, especially without a transitional agreement, not a good idea. EU has no unified capital markets (Tried the CM union for years, failed. Situation with the subprime banks in Italy and the other Eurozone periphery will probably mean that the CM union will be placed on the backburner). A sudden shock departure will lead to a lack of liquidity, and European companies won't be able to list in London and raise equity and debt financing via London.

Happy to tank downvotes (from you), and provide an alternative opinion.