H1 Amendment's impact on re-entry

[boringjazz]

My H1 visa was extended last year from August 2012 to December 2013. My current visa stamping and I-94 are based on extended petition. My company has submitted H1 amendment for Client name & location change 2 months ago and that is in progress. Now, I have to leave a US. 
Please help answer few questions related to same.

a. Can I re-enter US on extended petition or do I have to wait for H1 amendment to complete and for new approval notice/petition and get the visa stamped again?

b. If I enter on business visa, can that be then converted to H1 visa once the petition is received?

Please let me know !

Thanks!