Hi,
Firstly, disconnecting the ESXi host from vCenter will not affect any production VMs. Your VMs will continue to run however the VMs wont be able to utilize vCenter features like DRS, vMotion while the ESXi host is disconnected. I have done this in the past when the vpxa agent on the ESXi host is not updated, for e.g. you may see some state/orphaned VMs which you have already deleted.
Hope this helps !
-f10