Roseanne’s cancellation revolved around Roseanne Barr’s actions on social media, and The Conners didn’t receive a series order until Barr signed a deal that guaranteed a settlement that would cut off any further involvement and/or monetary gain from the franchise.
The Conners will happen without Barr involved in any way, although I suppose it’s possible that she could appear via flashback to scenes from Roseanne.
I don’t see the network bringing her back as a guest star to reveal that Roseanne left for some reason that didn’t involve her death.
Basically, ABC cut all ties with Barr in order to bring the rest of the cast (and the crew) back for the new show.