The I-94 governs your status in the US. If you leave the US, however, you will need an L-1B visa stamp in the passport in order to return.
The statement above is general in nature, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship.
Since your I-94 is what governs your authorized period of stay, you would in theory be violating no law by remaining here and continuing to work under the terms of your L-1B until the 2013 expiration. But if you plan to travel, you will need a valid approval and visa stamp in order to reenter.