Have you had a character brought back to life, or body hop?
Yes. Twice. Same character.
How many times are said character(s) brought back to life, or body hopped?
Aynea first died to Darth Metus and was summarily brought back by one of the Sith factions through a alchemic serum as an Energy Vampire. The second time was a voluntary "body hop" to a younger, -
living- body (as the original was still undead), courtesy of Circe Savan.
Have you had a character whose life has been unnaturally extended well beyond their years through some technique?
One of the effects of being an Energy Vampire is having your life extended virtually indefinitely (provided you are not ever mortally wounded).
How extreme have you had a character's life unnaturally extended through some technique?
Theoretically, she lives as long as she feeds.
Do you think characters that avoid mortality or staying dead, mostly adds, or mostly detracts from their relevance as a believable character?
I'd say it depends on the character and varies from concept to concept, but due to its overall cliche and prone to abuse, it's probably not the best choice for everyone. Part of being on a journey is moving toward a destination. Life
is that journey. Death must therefore be the destination if the journey is to exist. More often than not, this concept is what lends to the believability of a character concept or bio.
What is your general opinion of extreme life extension or habitual revives?
It always bites you in the ass. Whether you're a Sith ghost, an energy vampire or said "kark everything" and turned yourself into a Shard-droid, something is always being sacrificed in turn for that which is being gained. No one who tried to attain immortality in the SW-verse ever did so without consequence.
I have insofar voted in the majority in all questions but of whether or not I have used some technique to extend a character's life unnaturally, in which I voted the minority "Yes." I'm actually pleased with that as it means most people aren't Palpatine-ing en masse.