Re: Data protection directive
You can always make stuff no longer illegal, by changing the rules. There'll have to be an amendment to the EU treaties in order for the UK to leave - plus there's plenty of time to amend or draught any laws required.
Whether Europol data is shared is entirely down to the political choices made in the upcoming negotiations. Actually so is the link between freedom of movement and the single market. It is a political choice that I think the rest of the EU are likely to refuse full single market access without full freedom of movement - though you can make that claim and still save face by making the costs in loss of access so small as to be meaningless. This is pure politics - not the laws of physics.
As a guide to the readiness for cooperation in this area though, the UK now holds the new post of EU Commissioner for The Security Union - which has been defined as anti-terrorism and criminal intelligence sharing. Admittedly it was the Commission who created that job, and the member states who will decide the Brexit negotiations, but I doubt Juncker's too out-of-step with what they want.