There are articles on this topic, but I have decided to summarise everything in one, according to the tools we have in 2019 for the job. Provided you have the means mentioned, the task should take you up to 5 hours or less to get running again. It required however around 5 days for me to get there.
HOW TO: BOOT VMware vSphere Hypervisor 7.0 (ESXi 7.0 ARM) from an iSCSI LUN for the Raspberry Pi 4, Step by Step Tutorial with screenshots. Setting up the Synology SAN to allow the Raspberry Pi 4 to BOOT ESXi 7.0 ARM edition.
HOW TO: Install and Configure VMware vSphere Hypervisor 7.0 ARM Edition (ESXi 7.0 ARM edition) on a Raspberry Pi 4, Step by Step Tutorial with screenshots. From Download, Checking Media, to Completed Hypervisor Installation. Please check the requirements list before installation.