If they can find a way to get Jeff Kober to stick around for the fallout, they would be very smart to make him the liver donor. But Kober is in high demand for non-GH projects so the show likely would not write him a meaningful plotline unless he could clear his calendar. I'm guessing they don't mention the other possible candidates (like Ethan, Martin, Valerie, Lesley, etc.) because there is little chance of having those characters brought back.
Rick Hearst was originally intended to come to town only to comfort Molly and have a few sparring matches with Alexis, then leave again. Kin Shriner went and hurt his leg in some way and Scotty had to be quickly written out of the Heather story (acting as her lawyer) and the Ava/Cates story (as their co-conspirator). So they're writing Ric Lansing in as Heather's lawyer, expanding Rick's stay with the show.
The Kelly Monaco thing just makes my mind wobble.

She'd been a bit unreliable in recent years. If she was happy with her material, it showed--she positively sparkled with Billy Miller's Drew and Jason Thompson's Patrick, and I think she was enjoying her recent evolution into a "Mama Bear" for her kids with Dante as her co-parent. But it was very, very obvious when she did not want to play certain stories, like anything involving Sam and Jason. She would act drowsy, not make eye contact with the other actors, and just generally give the impression she didn't want to be there. She also goes through wardrobe "periods" where she'd wear black and brown all the time, but during the stories where she was happier you saw her in bright colors and florals.
The "anti-chemistry" between her and Steve Burton is palpable, and though the show has done everything they can to keep them out of one another's scenes, I can only wonder if their issues played a role in her seeming dismissal. It might have been purely a function of budget and the SB stuff might not have played a role at all, but I guess only time will tell. Given her good chemistry with Jason Thompson, Y&R would be smart to hire her as a new love interest for Thompson's character (Billy Abbott).