Samsung SSD 830 disappears
It may be fried, although 4 years is much shorter than expected lifetime.
When it was "was chugging along nicely" until now, I think a FW update will not succeed, nor be the cause of this stroke. It may be too full also.
I suppose that you already tried to see it in the Recovery Partition (start with CMD+R) and "repair disk" it with DiskUtility.