Approved Petition expiring in April 2014


I am currently in USA with a H1B petition valid till April 15 2014. However I do not have a H1B visa stamped on my passport currently . I need to travel to INDIA by Feb 15. I would want to know the following:

1.I am in EVVC model so what are the chances of approval if I have the client letter and Vendor letters as my petition is valid only for two more months.

2.My employer has filed for my H1B extension already in Premium processing. So will my travel affect the H1B extension ?

3.While taking the visa interview appointment should I take dates from old petition or wait for the approval to come and use the dates from the new petition . Do these dates really matter?