As part of setting up access to the vSphere+ / vSAN+ Cloud Service, a vCenter Cloud Gateway (VCGW) is deployed into your on-premises infrastructure and serves as a gateway between your vCenter Server(s) and the VMware Cloud Console.
If the VCGW has connectivity issues to the VMware Cloud Console for whatever reason, your infrastructure and workloads continue to run but you will not be able to perform any operations through the VMware Cloud Console until connectivity is restored.
UPDATE (06/21/23) - The period in which VMware declares a VCGW unreachable has been updated from 24hrs to 7 days. This means even if your VCGW loses connectivity, you will still be able to login to your on-premises vCenter Server and/or SDDC Manager without needing to go to emergency URL.
However, if you attempt to login into your on-premises vCenter Server(s) using the vSphere UI, you may be surprised to find the following error message.
While I will agree the user experience may not very intuitive, the hint is in the URL link below where it says "Still having connection problems?"
If you click on the link, you will be taken to the following VMware KB 83798 which outlines the issue, troubleshooting steps and most importantly a workaround to access the vSphere Client in an "Offline" mode via the emergency URL which is simply https://[VCSA]/ui/emergency
Before you can login, you will need to first request access for a vCenter Server user who has the vSphere Client->VMware Cloud offline login privilege, which by default, the administrator[at]vsphere[dot]local user will have and you can assign that to additional users if needed.
I also want to mention that the use of the emergency URL can also be audited like any other login to vCenter Server and a specific vCenter Event is emited called com.vmware.vsphere.client.security.LoginConnectivityCheckEvent, which can be seen in the Events tab as shown in the screenshot below.