To attempt to clear up a few things:
I think you're referring to the very ending of the opening scene here. Feathers fly up across the screen when Squall slashes Seifer's face, and if I remember right they turn black and the opening fades out. Really, I don't think this is symbolic of anything, rather it's experimentation with the FMV technology of the game. Alot of the opening scene of FFVIII seems experimental (the theme, the text, the way the name of the game is presented (flashes of it in between scenes), Edea fading in and out of focus, etc. etc.). Tetsuya Nomura even said himself that he added the feathers to Squall's outfit because he thought 'it would be a challenge to show in the FMV movies'[source below].
You remember that probably because Laguna says "Ultimecia exists in a time in which none of us can exist" (or something to that effect), she is too far in the future for any of the characters from the 'present' time in the game to survive, including Rinoa.
Also, Edea looks just as old as she should, after all she could very well only be in her late thirties - early forties. She especially looks her age when she goes back to being the good old 'matron' and dressing in her plain black dress. Furthermore, Edea was designed before Final Fantasy VIII was even conceived, thus lending light to why she may appear younger than she actually is.
Adel was sustained in a frozen reality, which explains why she did not age.
The only special relationship Ultimecia has with time is through Junction Machine Ellone. Without JME Ultimecia would have no access to the past or time in any way which discredits your statement.
Hyne also has nothing to do with this arguement, basically all it says is that Hyne made the world and his/her descendents are the sorceresses.
If I remember right, the part of the game you're referring to has Edea saying something like "a sorceress cannot rest in peace if she does not pass on her powers". She can't rest in peace, this doesn't mean she can't die and be uncomfortable in some sort of afterlife.
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I would also like to try and debunk some of the "Ultimecia and Rinoa both have wings!!!" stuff.
Tetsuya Nomura started designing characters before Kazushige Nojima and Yoshinori Kitase began to flesh out the characters and storyline. Nomura even had some input on the personalities of the characters (especially Rinoa's).
When Nomura first designed Squall he felt he needed to add something to him to make him more memorable, this is where Squall's scar came from. Nojima was left with the task of determining the origin of this scar in the game's story.
Nomura created Rinoa with the intent of making her memorable over her cute girlishness over a girl remembered over how beautiful she was, thus explaining Rinoa's attitude.
So, if Nomura had all that sway over the characters when the game was still in pre-production stages, it's plausible (although not confirmed) that the wings upon Rinoa's back were there all along and have nothing to do with Ultimecia's wings.
It's just an idea, a rather weak one, but I think it has some credibility.
Sources:
http://flaregamer.com/b2article.php?p=81&more=1
http://rinoa.nu/rinoa
http://www.wikipedia.org