Politics may be a bit screwy right now, but it's not insane, at least not yet in the UK, as much as people like to hyperbolise.
If you're currently living here, going abroad for a few weeks will be vanishingly unlikely to suddenly define you as no longer live here.
Oh yes it is. We have a nasty, dishonest and utterly incompetent government with free reign to do irreparable damage to this country, no thanks to our non-functioning and useless opposition party.
Meanwhile, our national press, who have never been anything other than dishonest and self-serving are in full frothing-at-the-mouth hysteria mode when it comes to Brexit.
I can't recall in recent memory a time in the UK when politics has been so dysfunctional and depressing as now.
All passports leaving the UK by official ports have been scanned by the UK Border Force for several years; at least five, from memory, and probably prior to their inception too.
They won't have a record if you departed in the dead of night from a small harbour using a yacht, but otherwise the database is fairly comprehensive. Even departures to outide the UK from my local flying-club airfield have UKBF in attendance ( I presume they charge for the 'service' ).
More likely everyone will have to prove their right to residence, and the border database will not be available to us.
And secondly, do you really believe the uk government capable of distinguishing between people who have arrived before or after a date? They don't have a record of travel for everyone in the country. Are you going to be keeping bills in your name from before 15th of march to prove your residence history, the same as for a bank account proof of address?
I've been in the UK for close to 10 years now and I definitely feel like this applies to me. I'm considering either getting a green card and moving towards citizenship, or just moving out of the country. These decisions are frankly insulting.