You should be able to re-enter without problems if you continue to work for the company that petitioned you. Your employer must file an extension request prior to the expiration of your status. Chances for an approval depend on specific facts and cannot be addressed in this forum.
You should be permitted to travel as long as you are currently working for the L1 employer. You need a valid visa and a valid passport. If you are in United States you need to apply for extension of stay prior to expiration. If you travel after the visa has expired you will need to obtain a new visa to return to the United States.