Heuffelii rosettes share a common root, so if you have multiple rosettes and one rosette blooms but the others don't, the plant will survive. The rosette that blooms, dies, for Jovibarba hirta, Jovibarba heuffelii and Sempervivum. I am hoping to one day see a singleton heuffelii rosette root survive after blooming and produce additional rosettes. I believe that this is possible, but have not seen it to date. (I've only had heuffelii for a few years)
There are exceptions or unusual cases. Sometimes you will have a Sempervivum rosette bloom and while blooming it will create offsets on the bloom stalk. The rosettes formed on the bloom stalk will survive, but the base rosette will not. It is relatively common to see a rosette of J. hirta produce additional rollers during the early stages of forming a flower stalk.
It is largely accepted that there is nothing you can do to save a blooming Sempervivum rosette, such as in the case of you having only a single hen of a type of plant. However, I have had some success with vegetative propagation of the plant if caught relatively early in the blooming cycle by dividing the blooming rosette into two or more pieces before the flower stalk is well developed. Some of these pieces will generate new plants and some may go on to bloom themselves. If a piece survives, it will often produce a cluster or group of new plants which should be divided when large enough to survive on their own.
Because J. hirta are so prolific, I have not needed to try this division process with a blooming rosette with them. So I do not know how well this procedure would work with J. hirta. Nor have I tried dividing a singleton J. heuffelii that is beginning to flower. I suspect that both heuffelii and hirta would react in similar ways to divisions as Sempervivum and intend to test this next year. Because it takes a little time for the divisions to recover into complete plants, I will wait until next spring to try this with heuffelii and hirta.
