The pro-Remain group TheCityUK already has a plan to limit the damage, insisting that the City can prosper outside the EU, provided the post-Brexit government launches a bonfire of red-tape, keeps the door open to foreign talent, and takes the lead in the G20, the IMF, the global Financial Stability Board and the Basel Committee.
They want unfettered access to the EU single market and passporting rights for the City, and this means either pushing for the Norway option of the European Economic Area (EEA), or a hybrid variant.
This safe-exit is a compromise, and an olive-branch to the EU since we would continue paying into the EU budget and accepting the EU Acquis. It would last until we have negotiated our bilateral trade deals with the rest of the world. It also means accepting the free flow of EU migrants for a while. This is incendiary, of course.