Lydia dies.  It has nothing to do with length of time, amount of ricin, hot water denaturing ricin or anything else you can possible think of.  All that matters is one simple thing.  Would Walt leave anything to chance if he could remove that possibility?  In this fictional universe, the answer is no.   Walt is/was highly inteligent and meticulous.  In planning the death of Lydia, he would remove any chance of it having any other possiblilty than what he choose for her.  Looking for proof?  The writers wrote Walter a P2P formula that does not exist.  Meth that is 99.1% can not be blue unless it contains a significant amount of impurity(s) but it "fictionally" exists in Breaking Bad.  Why not then, have a ricin formula that has a 99.1% chance of death?  Walt would leave not chance after his death that she could harm his family.  She died, end of story.  Just like everyone in the compound.

even if she dies due to magical incurable ricin, she could still hire a hitman to get revenge on walter's family. Telling her about the ricin made absolutely no sense, so either walter did something very stupid blinded by hubris (and lydia could survive and/or get revenge), or the writers didn't think this through (which would be a little disappointing from the series).

note: the hubris thing sounds like classic walter to me.

She simply has no contacts for hitmen, as Saul said, very few existed.

Ricin can be treated, but as far as I'm aware once the symptoms start showing and it enters the bloodstream, you're doomed. Keep in mind that Lydia was pretty much given pure weapons-grade ricin extracted by a master chemist, not those crappy castor beans that get mailed to Obama every few months. Lydia is screwed and she probably keeled over a day later.

Lydia was the final "big bad"- she put the hit on Walt. To work out whether she dies or not could be interpreted by whether we believe that Walter died in the final scene or not (I have a theory that supports the former). If Walter lives then she is dead- Walter has defeated her. If he dies, then we could entertain the idea that Lydia could have survived the "dual". 

If anything, the fact that we don't know for certain if Lydia dies, leaves the Walter survives interpretation open since the writing formula typically leaves one of the duelers alive (but scarred). 

OK, if Lydia somehow does survive, she may be in for a rough time of it, especially if she seeks medical help.

I don't see her doing what Mike Ehrmantraut does for medical help, which is either to go see a veterinarian as we have seen in "Better Call Saul" or Gustavo Fringman's physician like we saw at the end of Season 4 after Fring takes out the Cartel.

But that kind of medical attention is probably what Lydia Rodarte-Quayle would have needed to keep the fact that she was poisoned by Ricin quiet--and I don't see her doing that.

Instead, I see Lydia calling for an ambulance and being wheeled off to a hospital with an emergency room and once it is learned that she was poisoned by Ricin, count on Homeland Security getting involved and guess what, they will want to know how she got poisoned and she may wind up confessing to all her misdeeds at Madrigal Electric Motors.

And if she does that, following a request that Mr. Herzog made to the DEA back in "Madrigal" (BB S05E02) to root out any elements tied to Peter Schuler's criminal work in the foods division, the DEA and their German, Czech and even Chinese counterparts will work to expose Lydia's contacts in those subsidiaries and they too may have connections to Lydia's other criminal activities, from getting the Methylamine from China to Long Beach, from Long Beach to Tulsa, from Tulsa to Houston, and from Houston to either Fring's, Walter's, Declan's or even Jack Welker's organization where they use that Methylamine to make Meth, and then use Lydia's connections to get that Meth out to Europe and Lydia's contacts at Prague and possibly at Hannover and Madrigal's world HQ.

And if Lydia survives, she's going to have a hard time doing it.

All of this to say she'd better die

Unless I missed it in my scroll, she also put out a hit on Mike and a crew member, with the latter being killed. Given how fussy she was in every diner scene it was a well deserved ending for her. Let’s presume she’s dead, we’ll all feel better about it unlike Lydia.