^^^Taking the pills suggests to me that Walt gets taken down by a recurrence of his cancer. (I don't think there are any pills that treat ricin poisoning.) Not seeing Skylar, Junior and the baby is suggestive too, that he sacrificed his family in some fashion or other too.
A gun doesn't suggest that he's facing off against Hank. Even a big gun isn't going to help against the US government. Besides, as last night's episode showed, even when or if Hank figures it all out, he's a huge loser. The big faceoff, if that's the finish, has got to be against somebody who's at least a respectable opponent. My guess is Mike.
Jesse is just too well established as a weakling puke to be a worthy foe. Just look at how he cried like a girl. A sentimentalist might think that having decent, humane feelings are a plus. But the true secret to a compelling character in these modern times is winning.
Walt's a winner and Mike's a winner. Jesse's a loser. Chances are that Mike will lose, because he wavered at killing Lydia just because she was brave for her daughter.
Mike's return centered upon the feds taking everybody's money, which didn't just hurt him in the wallet, but opened him up to people turning. They may be standup when they're paid, but when they're supposed to do it for free? And obviously they could take the money because they got the account information. Thus we have the situation where the whole plot is technically motivated by the chance discovery of the bank account numbers when Walt wrecked thed evidence room! There's enough irony there for an anvil.
PS Good episode for showing Jesse and Mike. The most "interesting" moment with Walt was the threat of marital rape. Skylar needs to think through what she's going to do. Wanting to remain pristine was really too late when she helped Ted cook the books. That is a crime after all. And she's the one who did Ted, in more ways than one. Playing shrinking violet now seems both stupid and a tad hypocritical.