IME, hypericums are one of the toughest plants on the planet - will tolerate just about any kind of soil except boggy, quite cold hardy, will take both full sun and part shade and, if the gardener so inclined, difficult to kill :-)) So not at all sure why yours would not have survived, unless you experienced the winter from hell last year, as many did.

We sell a great many of these shrubs at my nursery in the full assortment of berry colors. They are just selections of Hypericum x inodorum, so hardy to zone 5 and rust resistant (a big bonus for any St John's wort!). If you like it, I'd try again.

Thanks! I'm going to do that.

If the kind you are asking about is an H. x inodorum cultivar you may want to do some more reading about it as I am looking at a generally pretty good seeming print reference that - rightly or wrongly - is indicating USDA 7 for that cross. The one you tried before may also have been a kind that does not come through every Zone 6 winter - or maybe even most of them. A good policy is to assume that commercial sources in particular are rating plants one zone too hardy, so if a plant is rated USDA 6 it may not really be able to last in that zone. (Also if someone is saying a plant is hardy to that zone then really they are saying that is where it is on the borderline of hardiness, with there being failures likely at least a small part of the time).

I heartily endorse H. frondosum 'Sunburst', the flowers are great, the foliage is semi-evergreen, and it's a native of my area. If you can't find Sunburst, any frondosum is much the same.
I grew it in Oklahoma, in an area where the ground would occassionally flood for a day or two, but it could also become sweltering hot and dry in the late summer. It survived reaching -27F with snow cover one winter.

Here is a link that might be useful: MO Botanical link to Sunburst