okay these are my thoughts, but they'll probably change from reading interviews of all the cast members(they always do)
so umm i'm not sure okay so dont go all crazy. just my thoughts.....so shannen leaving was planned way before 3x22 AHBL. so gradually in season 3 the writers had to think how will this character, prue, exit. would it be her floating up to heaven or something? tragic death? an elder or whitelighter? so my guess is the season finale had to huge, a cliffhanger. so that season 4 would be huge. people would wanna know, "what happens next?" you know. 3x22 was written by brad kern and directed by doherty. and i think i read that doherty wrote a little w/kern. prue's death is a really good story line and a jump start for season 4. i don't think the writers, or whoever does the show, were like "oh she's leaving, we're make her character die, a horrible and painful death." nooo it wasn't like that, this episode is a freakin huge, HUGE part of charmed history. maybe prue in a happy-ever-after thing was boring, so you know, maybe this episode would shock people. making you watch it over and over again(i know you do) i mean, who the hell watch's forever charmed over and over again, 8x22 was so sad, i don't know why. anyway....AHBL was a good, awesome, holy crap freakin....omg i can't even....ha it was...let's just say good work shannen, amazing. i'm stunned til this day....
plz don't shoot me...