Helseth.hes the man.hes the king.hes...dead? It kind of bothers me that I have to assume the standard fate assumption of "oh he was assassinated.oh a portal opened up and overcame his city". So what do we know?

As far as I know there is no information if he or his mother are alive or dead.

I was wondering much the same thing myself. I haven't found or heard any information about him or his mother, or his sister Morgiah either. The only information in game is regarding Helseth's supposed neice, Karliah.

I find it a bit odd they wouldn't mention something concrete about the fates of Helseth, Barenziah, and Morgiah, even if just to confirm their deaths.

Barenziah's Crown was dismantled into its individual gemstones and scattered to the winds, so it's safe to say the Argonians got her. And if Barry bit the dust, it's safe to say Helseth did too. Morgiah would've died the moment the Thalmor rose to power.

The where and how of it is up in the air, though. Maybe they were fleeing to Solstheim and were ambushed in the dead of night, or maybe he died the way my Nerevarine did the deed, and slit his throat while he sat on his throne. That was a nice robe. It had to be done.

Yeah, I assumed this too. The Thalmor being the pure-blood fanatics that they are, as well as the fact they had to kill all the ruling families to gain power, means that would have been 2 strikes against her.

I assume Barenziah and Helseth are most likely dead too, it just would have been nice to have some closure.

http://www.imperial-library.info/content/guide-better-thieving indicates that the crown was stolen by someone alive during the Oblivion crisis. Obviously it's not likely that this Wulfmare had anything to do with it, considering the veracity of his other tale, but I don't think that he'd just make the entire story up. It seems that the crown disappearing is a somewhat known event (at least among thieves) that he's just taking credit for. If the crown was never stolen, it would be quite easy to dispute the book fully.

Thanks for the link, haven't seen this book before

Anyway that means that we know absolutely nothing about Barenziah and Helseth, except for that Barenziah should be nearing 700 years right now (if she's still alive) and that's old even for a Dunmer... She was even feeling old back during Tribunal, so I would think she's dead by now.

Helseth could be in any kind of situation, however I'd think he'd be dead by now. During Morrowind Helseth tried to move Morrowind more and more into the Empire, that move has obviously failed with the Empire falling apart and the Argonian invasion. I'd imagine he'd be a ripe target for a great many people, Argonian and Dunmer alike. It also doesn't seem like the Empire is capable of offering a great amount of support to the Dunmer. So his greatest allies are likely useless. Of course I'm not sure that this means Helseth is dead, it just doesn't seem that unlikely to me.

Morgiah is either captured or dead, the only place she could have run after the Thalmor uprising is the Empire and then came the great war where she would have been a target again. She has a few options.
1. Skyrim (Where she isn't)
2. Hammerfell (Unlikely because I believe we would have heard something about it)
3. High Rock (still part of the Empire so unlikely)
4. Morrowind (But that would only be logical if Helseth was alive, and even then a stretch because I don't think Helseth would appreciate his sister showing up)

I think it's most likely that they are all dead...

Agreed, Barenziah most likely dead from age and Morgiah most likely dead by Thalmor. Helseth is hard to say. Of course a prime target for a great many people but should not be underestimated. He might be dead but might just as well pop up when we least expect it.

I have a feeling Red Mountain got the better of the royal family. At least the Queen had a nice run

Oh just you wait kiddies for the first Skyrim DLC when Vehk and Helseth show up on the mean streets of Windhelm in a bad cop/bug-armored hermaphroditic cop duo armed with spears and the answer of what REALLY happened to the Dwemer (hint: calipers).

It is the missing ingrediant, now where did place that yarn?

The more interesting question is what happened to Morgiah's firstborn, assuming one existed?

saw him die in the morrowind expansion tribunal, someone killed him for his sweet stuff,

Bethesda tries not to reuse characters that you may have killed in the previous game, its why vivec "disappeared"