Sorry to see your loss.
From my own history with my EX4100, I suspect you’ve identified your way forwards: just use a JBOD. (And another drive/device, preferably offline, for mission critical backups.)
My EX4100 is happy swapping disks in and out of a JBOD. By shutting down, doing the physical swap, and then following the prompts on the next boot. At least you get mass storage, on a NAS, this way. (Be sure to name your folders differently to avoid any potential for clashes at any stage.)
With a JOD, you’ll just have to manage file backups/redundancy via another drive/device.
From what I can tell, none of the consumer level NAS devices are equipped to handle RAID-tastrophies. But they do tend to work fine while enough disks are healthy enough to support the established RAID function. They won’t necessarily tell you of any impending RAID failure though; they leave your expertise to determine that and if you don’t have it, the expertise, then you’re screwed. They usually give you access to SMART to monitor disk health, and some might even prompt warnings from SMART, but most don’t seem to. So…
They work while they work but you’re sh!t out of luck when they don’t.
I suggest a much higher shelf or a tightly strung pair of boxing gloves for the next setup.