Don't panic (Dad's Army style) but vote early and vote often ;)
On a serious note I am trying not to worry but I do
Put simply we cannot know what will happen after an OUT vote.
Based on the sample of DH who is as French establishment as they get it won't be pretty. We've had grumbling of "de Gaulle was right, we should never have let them in" already.
The vote this summer would be followed by 2 years of negotiations. Not with the EU as such but with 27 governments some of which including France and Germany will have elections coming up. And EU apparatus itself. And they will be spitting mad.
I fear they won't run along the lines of what's in the best interest of all. "Pour encourager les autres" anyone who doesn't contemplate their own referendum would try to make it as painful for the UK as possible.
And soon enough you will enter the tit for tat
Imagine the UK government moves against migration from EU 8 +2 and given that EU doesn't allow discrimination among member states in bilateral treaties
Whatever measures are introduced to say Ruritanians in the UK may be repeated against Brits in France
Right now we get residency after 5 years as EU citizens. But we won't count as EU citizens within 2 years of the vote. Then who knows what residency rules wil apply. And they will be applied according to domestic politics of each country.
So I encourage all who can to register to vote and get your friends to do so to
It's easy now. The trickiest bit is getting a British passport holder as countersignatory if there are none around
If you are registered make sure they have the correct address. And keep registration current - you need to reconfirmed each year
And do it now
It took me almost 3 months to register at last election and then it took my borough so long to send the ballot papers that I didn't get them in time to vote :/