I’m wondering too. My case is different, with Unraid and HassOS running on Proxmox, I don’t like to delay the start of HassOS by several minute (I need my automations back ASAP), or that I have to reboot HA XX minutes after it started.
I also have a NAS that I use primarily for backup purposes which is down during daytime. But to be honest HA doesn’t have any issues reconnecting when the NAS is powered on. The only issue I experienced is that when the NAS is down, when I want to access files in the /share directory it takes some time. Obviously because it is waiting for a timeout connecting to the NAS. Whenever the NAS is online the connection is re-established automatically.
If your setup does not reconnect automatically you could consider connecting from your NAS to HA instead. You can do this by installing the SAMBA add-on, then mount HA from your NAS and mirror a backup you created locally on HA.