Not sure about WSs, but my tri-form PB needed it to be able to last even a single fight in human form. That might change at high levels when you can get some serious EndRed slotting in, but not in the 20s/30s (for me at least!).
Warshades don't need Stamina, assuming you're going triform.
Just make sure you slot up Stygian Circle!! 
Stamina won't have any affect on Nova or Dwarf form (because it's an Auto power) so if you're planning on ignoring Human form you can leave stamina. But if you want to fight in humnan form, I'd say it's a must-have - it's just painful without it sometimes. At least until you get Conserve Power.
I've not tried Conserve myself. Can anyone say if it's a good alternative to Stamina?
"The Hamidon is a what what of what?" - Brian the mission guy.
Conserve Power does the job nicely, but is PB only, not for WSs - and it's only up for a fraction of the time, even fully slotted.
While it's up your end problems are over, but unless you want to spend a fair amount of time waiting for it to recharge it can't be used to fully replace Stamina.
Oh yeah. My post was based on my xp as a PB, rereading I see the OP wanted WS advice 
"The Hamidon is a what what of what?" - Brian the mission guy.
So for WS's you can skip stamina then, (as long as you take Stygian circle).
Finaly a powerset where you don't have to sacrifies 3 powers just so that you can use your other powers. I honsetly don't understand the point with stamina in the first place. Why not give us stamina's end bonus in the first place and let us have more fun with more fun powers instead. ( End of rant. )
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Just got my first 50 and deceided to make a WS. Since I obviously never played a Kheld before I was just wondering if they suffer from end limitations like all other ATs and requier stamina.
So will I need to take stammina to be able to pay my WS full out?
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Kheldians suffer all the same limitations even more than other ATs.. 
i found on a human/dwarf ws and then on tri form that stamina was useful, i also found that there are enough powers you can drop to make it fit - its slots i found difficult to get to fit.
but as mentioned, Stygian circle should be taken before stamina - its got a bigger return however needs a dead guy, which sometimes with a human shade is a bit problematic as they are fairly low damage contrasted to a nova formed WS.
note: i am primarily a human warshade even with the 3 form version
@ExtraGonk
Just got my first 50 and deceided to make a WS. Since I obviously never played a Kheld before I was just wondering if they suffer from end limitations like all other ATs and requier stamina.
So will I need to take stammina to be able to pay my WS full out?