do you think Plusnet will ditch ALL landline including non-business ones.
I would say yes, that's very likely.
The analogue telephone network ("PSTN") goes stop-sell very soon, in September 2023, and will be completely switched off in December 2025.
If Plusnet want to continue selling voice services on FTTC (which becomes SOGEA without voice), then they will have to build a digital voice product to make phonecalls over the top. This could also give them digital voice on FTTP.
However, why would they go to the trouble of doing that, when voice is a low-margin and declining business? Instead they will say "sorry we don't do voice any more. If you want voice, go to BT" (who already have their digital voice platform up and running).
Of course, you could also go to Sky or Vodafone or Zen, all of whom offer digital voice already. Or you could move your voice service to a third-party VOIP provider and make it completely unbundled from your broadband.
The other big provider which doesn't offer digital voice is Talktalk, but because they have their own MSANs in telephone exchanges (which are capable of doing both DSL and analogue voice) they may continue to offer analogue voice for a while longer; they can do so even after Openreach have turned off their analogue phone exchanges. But sooner or later, they'll have to make their own decision as to whether to turn this off too.
When they do, perhaps they should change their name from "Talktalk" to "Typetype"