According to Birgitte, the heroes are bound to the wheel and live in Tel'aran'rhiod until reborn. The Forsaken seem to be able to enter Tel'aran'rhiod at will. Can they kill the bound heroes? If so, why don't they?
At least according to Brandon Sanderson, 'final' no-reincarnation death in Tel'aran'rhiod doesn't happen to humans. Some in-world people think it does, but they are wrong.
If people can be removed from the Wheel by dying in the Wolf Dream or the Dream World when they're there in person, how is it that there are any people left, if there's been an infinite number of turns of the Wheel?
They actually can't. That only works on wolves, regardless of what some people think in-world. I thought like you do, but Maria was quite firm that RJ said it couldn't happen, even in the World of Dreams. (Or even with balefire—which I thought would also remove people. Maria explained that I was wrong, and RJ was firm on this one too.)
Unknown, but probably.
There's nothing direct in canon that addresses this - Birgitte being ripped out of Tel'aran'rhiod early is the closest, and she straight up admits she has no idea how thorough the ramifications are - whether it un-bound her from the Wheel or not.
However, according to Hopper, wolves who die in the dream die forever. After he catches up with Perrin, who just (while in Tel'aran'rhiod) chased Slayer to the Tower of Ghenjei:
Cub foolish, digging in a groundwasps' nest. This place is evil. All know this. And you would chase evil into evil. Slayer can kill.
Perrin paused. There was a sense of finality to the emotions his mind attached the word "kill" to. "Hopper, what happens to a wolf who dies in the dream?"
The wolf was silent for a time. If we die here, we die forever, Young Bull. I do not know if the same is true for you, but I believe it is.
The Shadow Rising, chapter 28, "To the Tower of Ghenjei"
Also, when Nynaeve and Moghedien stalked Gaebril in Tel'aran'rhiod, Moghedien was quite clear about her concerns:
"...They are here in the flesh, not dreaming! They are using things you have never dreamed of! They will destroy us if we stay!"
"They will kill us," the other woman mumbled faintly, and nearly unintelligibly through her sobs...
So a member of the Forsaken clearly felt that death in Tel'aran'rhiod was final.
The Fires of Heaven, chapter 55, "The Threads Burn"