is my old I797 still valid until I get new one approved?

[Dharmateja]

Hi,

I have a valid I797 and stamped visa which are valid till Dec, 2019. Now my current employer is willing to file a cap exemption using my other company's approved I797 copy.

My question is,

1. What IF my current employer receives RFE from USCIS and doesn't respond, are my old I797 and visa valid? Can I travel with them and work with the company who filed my original petition?

2. What if current employer receives I797 approval, then my old I797 will become invalid?

Thanks,