Re: Don't worry
In this particular area, you couldn't be more wrong. Whatever people's feelings/thoughts on the relative balance of economic and political power, the UK are in a very strong (the strongest?) negotiating position here.
UK POolice and intelligence services apparently put in a disproportionate amount of Europol's data. I believe we may also be their heaviest user. We also have pretty good joint intelligence relationships with the other big European intelligence players. As well as stronger intel relationships with the US (and the rest of 5 eyes) than any other EU nation.
There is no barrier to continuing whatever sharing relationship the two sides want. The strong signal from the EU is that they want/need our continued cooperation - this signal is that we couldn't keep the financial services brief at the Commission (that would have been ludicrous), so were given the Commission for intelligence coordination. That strongly suggests that the political will exists.