H1b to h4 stamping


Myself and my wife going through tough time now. Need your suggestions on the below.

We both working in same company and we have got our h1b stamped last year. We are unable to find suitable opening for my wife in our company. I have travelled to US two months back. And we dont want to be get seperated till she get project as there is no positive sign for that.

Now our concern is, if we apply h4 will US embassy reject her already stamped h1?

Also how much time it takes to get h4?

If stamped h1 revoked, is it possible to apply again with existing approved I797?

your suggestions are appreciated!!!