Short answer: if you vCenter trail expires all hosts will disconnect, so nothing can be managed anymore in vCenter. If ESXi trail expires the configuration gets frozen and no changes can be made including any new VMs or powering on VMs. VMs that were running when the license expired will keep running.
vCenter:
When the license or evaluation period of a vCenter Server system expires, all hosts disconnect from that vCenter Server system. The virtual machines running on the disconnected hosts remain intact. Until the vCenter Server system is assigned a new license, you can manage the virtual machines on the disconnected hosts by logging into each host separately. After vCenter Server is assigned to a new license key, all disconnected hosts reconnect to the vCenter Server system.
https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vcenterhost.doc/GUID-F2B7886A-A4A6-...
ESXi:
For ESXi hosts, license or evaluation period expiry leads to disconnection from vCenter Server. All powered on virtual machines continue to work, but you cannot power on virtual machines after they are powered off. You cannot change the current configuration of the features that are in use. You cannot use the features that remained unused before the license expiration.
https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.esxi.upgrade.doc/GUID-17862A54-C1D4-47A9-88...
