Sedum bithynicum 'Sea Stars' is winter dormant, where hispanicum is evergreen. Sea Stars is also suppose to reseed easily. What a great sedum.
The blooms are also different between the two species.
Do you know what killed it Julia? Or did it just go dormant? Did it bloom? I think blooming is the key to keeping it around for us in the PNW. Not sure at what point in spring the seed would germinate? If it bloomed maybe you will have seedlings?
I bought it last summer, in bloom, and planted it but I think it got too dry. I will hope for seeds!!! It was blooming then just disappeared in the summer. Think it went dormant at that time?