Legally, H1B sponsoring employer has to withdraw H1B once the H1B employee leaves. So yes they will/should withdraw H1B petition once you leave.
In your case because you have never worked for the H1B sponsoring employer on H1B status, technically your H1B is considered never activated. USCIS can deny cap-exempt on basis of above. That said, there are cases where H1B beneficiaries were approved for cap-exempt H1B by another employer even if they never worked for the original sponsoring employer so it just depends on the adjudicating officer.