If some one tell me on the below situation

L1 visa holder leaves United States after his project over. Can a person on L2 visa which is dependent visa continue to stay in USA to complete his studies until his I94 expires.

As long as L-1 is not terminated from working with the company yes, but this L-2 will not be eligible for OPT. If he/she wants to find a job during the OPT term, he/she should file for change of status to F-1.