L1 to H1B - If i need to go before H1B Approval

[dheera]

Thanks to timely answers from the members of the forum.

I am currently on L1B from company A working in US on a assignment. I am planning to file for H1B through Company B in April 2009. My L1B is valid till 2009 Nov. My current assignment may finishes between May 2009 to Nov 2009, My current employer may ask me to go back to my home country in this period.

I have following questions:

1. Which is best option to apply, with COS or with out COS ?

2. If i apply with COS, Is it mandatory to stay in US till my H1 petition is approved ? If my assignment finishes before I recieve my H1 petition approval notice and I am asked to travel back to home country by my current employer , what happens to my H1 application ?

Thanks in Advance,