If Bonnie was became a vampire, would Bonnie loose her powers?

Maybe, Maybe not, i dont know sometimes in show they make a statement to only prove the opposite later, it could be a twist revealed later in the game...
Maybe it's just against their rules for the witches, so they let other witches think they couldnt be both vampire and witches, and maybe in fact technically it is possible, but its saw as an abomination like being vampire/werewolf... and we know witches want to keep the balance of the nature, so they made this rule, because a witch/vampire could be very dangerous, so they tried to keep this from happenning by warning witches they would loose their powers if they wanted to become vampire, so witches never tried to... who know ?
But from what we know, it's not possible, Rebecca said so...like she said she buried her mother, but what if Esther is in the coffin as a witch/vampire ? ;) that would be a twist.
But it could also be the other one, Ayana, maybe she was more powerful, she did seems to know more, and the necklace was her first if i remember ? there was a strange scene with her and Rebecca who tried to touch it and it burned her...maybe we are sensed to believe it's Esther in the coffin because of the necklace, but it will be Ayana instead ?
Lol, well i should stop with the speculations ^^

Yes. In 3x08 Rebekah stated that you can be one or the other but never both. =D

I think she would have to lose her powers before becoming a vampire :)

When you say Bonnie you keep thinking about a selfless girl with witchy juju. And i think the writters see this too.They said that Elena will turn at some point into a vampire so i kinda can't see Elena watching Bonnie grow and die.It would be odd because she doesn't want to lose anyone else that she loves and when she will be a vampire this will be magnified.The same goes for Caroline.It would be so unlike them so watch their best friend grow old and die.When Bonnie 'died' Elena told Stephan to give her blood but it was too late and she had her hear so broke then.And Caroline said she will eventually force her father to feed.If it wasn't Elena she would have done it so if Bonnie is dying both will try to turn her.If Bonnie dies not turning(like in a fight or something) would really crush Elena and Caroline(if they are vampires or just Caroline the sadness that they will feel wil be HUUUUGE). They turned Caroline,Elena will defenitly turn(Salvatores) and it would be kinda stupid to break the bond between these 3.
Also in one interview KattyG said that Bonnie will have to face Klaus,but not in a way we all would expect.Until now we only had the dream scenes so she didn't face him yet.Also she got attacked by Esther and she will have to tell Klaus something.And as she goes to his manison she talks to him than Esther appears and sees them.She will know that Bonnie's a witch after all she attacked her.Esther said she came there so forgive him and i don't think she will enjoy seeing him as the only hybrid around~all alone~.Esther is powerful and she will cast some spell and turn Bonnie into a hybrid~vampire with witch powers.We are so into the hybrids that it would be stupid not to explore the witch/vampire hybrids.The only witch that would make sense to turn would be Bonnie.
So Klaus won't be alone anymore,Bonnie&Caroline&Elena will have each other forever,Bonnie won't be alone(Grams/Abby thing) so it's a win win win.

As i said a witch/vampire storyline shouldn't be avoid and Bonnie is the only witch that we know since the beginning and come on Elena/Caroline/Bonnie 's friendship is unique