I moved to FTTP in March but opted to retain my land line, going digital voice.
The LL number digital voice migration did take place on the day about an hour after the BB FTTP was activated and the FTTC BB went off.
Funny enough, I still have an old analogue phone connected to the copper LL and to this day, some 7 weeks later it still has a dial tone!
Checking with 17070 advises of a circuit number, not my original LL number, which by sequence is on my local exchange, unable to dial out and ringing this number gives unobtainable tone!
So to answer your question, no, the copper LL, certainly in my area is not physically disconnected/removed, my POTS is/was UG DIG supply.
My rather long recent FTTP migration saga is here which you may find informative.
https://forum.kitz.co.uk/index.php/topic,26792.msg449417.html#msg449417