You can get lightsabers with red crystals as mission rewards later on, that you can still equip as long as you don't pull the red crystal out that they come with. I know I've gotten them on my lightside 33 Sorc.
So you CAN keep playing with a red saber, but you'll have to work at it a little harder, and you won't be able to always have a state-of-the-art crystal, but you won't have to stick with your +1, either.