On L1B visa. Came in July 2012. Will return on mar 2013.
Wife and child in india(india passport holders). Might or might not come to usa.

What should be my filing status?

If you arrived on or before 2 July 2012, you can file jointly regardless of WHERE your wife is located, but, by filing jointly, you MUST report ALL world-wide income. You can mitigate the taxes by claiming the Foreign Tax Credit (Form 1116) for taxes paid to your home country.

If your wife and son come before 31 December 2012, you can also claim your child as a dependent and get the $1,000 Child Tax Credit. They WILL need to apply for Individual Tax Identification Numbers (ITINs) by submitting Form W-7.

However, if you arrived after 2 July 2012, then you must file as a non-resident alien because you have not yet met the Substantial Presence Test (SPT) and will NOT if you leave by March 2013. You must wait until sometime in MAY 2013 to meet SPT, and you will NOT meet that requirement if you leave in March 2012.