Well, the real point of Tasha's passing (intended or otherwise) is that death isn't
"meaningful". We place meaning behind some deaths, we use patriotism and doing one's duty to as icing to sweeten up the deaths of soldiers for example, but in the heat of the moment somebody can be doing a job one minute and simply be gone the next. Ultimately it is those of us who left behind attribute meaning to death, we ascribe honor to those passed, mostly as a means of coping with our own losses. But at the most basic level a human life is gone. Finito.
"Skin of Evil" is incredibly clever in using this. We see Tasha doing her regular duties on the Enterprise, we see her talking with Worf about a competitive event they're both scheduled to take part in soon, we get a flavour of her friendships, the minutea of her day-to-day life, we see her being part of an away team mission that is just like any other away team mission... and then she's just suddenly and irrevocably gone
. And that's what gives her death a real and very human impact.
On a fundamental level I actually find her sacrifice in "Yesterday's Enterprise" somewhat trite. It's what we expect
fictional characters to do when they face death, it's caught up in the mythology and romance of sacrificing your life to save others, noteable and honorable things. But for my money, it just doesn't present her death as well
as "Skin of Evil". The lack of any foreshadowing is what makes Armus killing her such a Wham Moment for the viewer, and gives it a (perhaps unintended) impact and emotional connection. Denise Crosby might have regretted her decision to leave so soon in the years afterwards, but she should at least take solace that if her character was going to die, then what a way to go. The character of Tasha Yar is more memorable for her death than she ever will be for anything she actually contributed to the series while she was still alive.
(My own older brother, *not* a Star Trek fan like myself, still talks fondly of having watched Season One when it first went out, and cites Tasha's death as one of the most memorable things about it. Which means "Skin of Evil" did its job well. It's shock value, but good