I can't believe we only have eight weeks left to guess how it ends. IMO, plot-guessing is the best thing about following Breaking Bad. I'll never get this chance again, so I'm going for broke.
We know from Rolling Stone that Walt returns to Albuquerque in the opener in order to "protect someone."We also know that Gilligan considers the ending [paraphrasing] "a victory for Walt, although it might not seem like one." I think the new meth distributors (still underused) will be pissed about Walt retiring/disappearing and are gonna want someone to fulfill his bargain. Good thing Walt gushed about Jesse being "the second greatest meth cook in the world."
Jesse, I think, will hook up with Hank (a pairing the writers can't resist), and will try to bring Walt down legally until he disappears. Jesse will interrogate Saul about the disappearance, but Saul, in trying to persuade Jesse not to mess with scary-ass Walt, will let slip that Walt is a kid-poisoner. Saul, being half-implicit, will save himself from Jesse's wrath by giving up "the guy who vanishes people," so that Jesse can hunt Walt down and kill him. Just when we think the big showdown is on, the meth peddlers will kidnap Jesse.
Walt will be oblivious to the kidnapping, spending his final days in NH (he's coughing and taking pills in the flash-forward), and in regret/repent (he arranges his bacon nostalgically, gives the waitress a generous tip). Something needs to happen to get Walt back to ABQ. Best guess: Hank tracks Walt to NH. Hank will have tailed Jesse, so he'll know that Jesse visited Saul before he went missing. Hank interrogates Saul, Saul gives up the "vanishing guy," the vanishing guy gives up Walt.
So Hank tracks Walt to NH, where Walt gets the jump on him. Hank then tries to save his own life by guilt-tripping Walt about the mess he left in ABQ: countless deaths, an orphaned family, etc. (especially potent if the bacon theory proves true, or if Walt Jr.'s car crash ever happens). Either way, Walt would learn from Hank that the blue meth is back on the streets, and from that he'd know that Jesse was kidnapped since he was adamant that he'd never cook again.
So Walt spares Hank, escapes, and returns to save Jesse as a way of repenting in his final days. Well, whoever he returns to save (if indeed that's what he's doing), it's a fair bet he'll succeed if the ending is like Gilligan says. Maybe since Walt is fond of giving people choices, he could save Jesse, confess to Jane's death, and then give Jesse some options: "A: Turn me in, B: Let me go and I'll die anyhow, or C: Take this gun, and kill me right here." The final scene could be Jesse's decision. (And since this is practically a fanfic: maybe a mirror of the famous shot where Jesse kills Gale, only this time with Walt and with no hesitation in Jesse's eyes before he pulls the trigger). /end crazy fanfic.
No idea what he'll do with the ricin. Or how I'll cope when it's over.