If Elena becomes a vampire the salvatore boys might not be interested in her any more because once you become a vampire all your emosions are heitend they will probably wait a couple of years until a new doppelganger from elena and fall in love with

There's not going to be a new doppelganger. Elena didn't have a baby before turning into a Vampire. I didn't get your question though.

As NiazAbedini & clairmxxx already siad, there' won't be another doppelganger, Elena ended her line (if we won't suddenly learn that she has a missing sister or close cousin.). You should explain what you mean with your question, becasue this question really isn't clear... Why wouldn't Salvatore brothers be interested in Elena when she'll be even more in love with both of them...?