Your wife can certainly travel and come back before you change employers. She should not travel while the H1B petition is pending as this will void her H4 application. She should file for the H4 together with your H1B petition because that way her H4 approval will coincide with your H1B approval which should be good for three years.
After you get the new approvals, the first time you exit the US, before coming back you will need to stop by the US Consulate in your home country so a new visa can be issued that coincides with the validity dates of the new H1B and H4 approvals.
We would be happy to assit you and you newremployer with the H1B process.