BT's subsidiary Plusnet is finishing Line Rental Saver. Is BT going to do so too? They may be the only ISP now providing this discount.
You're not likely to get a definitive answer here in advance of any public announcement by BT. While it was a decent discount when first introduced, the LRS has been devalued to the extent that it's probably more trouble than it's worth for BT as well as customers. My prediction is that it will sooner or later be towed away and crushed.
There is still a reasonable saving with LRS, you get one free month, pay for 11 and get 12 months.
Any increase in normal line rental during the LRS only applies at the end of the 12 month LRS.
After I moved to Digital Voice, I found that I was no longer able to use LRS any more.
So I guess that as people are moved onto Digital Voice over the next few years, it will disappear.