H4 to H1B without H4 being stamped

Hi, I am on H4 visa in US now. I came here initially on L2 visa since my husband was on L1 last year and later changed to H1B in October 2012. Since then my visa is also changed to H4 and we have not yet got the visa stamped. This year we are planning to apply for H1B for myself. But my concern is

  1. Is it ok to apply for H1B when my current visa H4 is not stamped.

  2. If so what will happen if I go to India in case of any emergency before October 2013 provided my new H1B petition is also approved by USCIS ? During stamping will my H4 be cancelled and H1B be stamped or would there be any other issues?

  3. If my H1B is stamped and H4 is cancelled then can I not travel back to US until October 1st 2013.

  4. Or will my H4 be valid till H1B begins.

Please could any one clarify.