Season 6 & to a greater degree, Season 7, are both so screwed up with the characters I can't even wrap my head around it.
Again, with my theory, Willow simply would have been in shock and would have been unable to feel Tara's pulse because at the point she saw the blood and the bullet hole, she would have already been thrown into the state of anger, shock, and saddness that she was in in the real episode. She still could have contacted Osiris, and he would have told her no, but I really doubt he would have said something along the lines of "Tara isn't dead, stop." He probably would have let the events play out.
I absolutely love your ideas Morbius!
Why couldn't we have had something like that on the show?
Why did they have to kill my beloved Tara?
.......Sorry, I get emotional when it comes to Tara