H4 to H1 COS

I am in the US on a H1 Visa. My wife is in India and she has an approved H1B petition from Oct 2015 to Dec 2017. She hasn’t stamped that Visa yet since her employer doesn’t have a project to travel for. She is gonna travel on H4 late September or early October this year. I am planning to do a Change of Status to H1 once she gets here. Can her current employer withdraw the approved H1B petition. If they do will it impact her CoS decision?

Yes, current employer can withdraw their petition.

However, another employer can still apply for a cap-exempt petition + COS for her using old approval copy as reference and proof of having made through the cap.