The latter is more likely if the plant is small or weak at the onset of flowering, although even large and healthy, some bamboos such as Fargesias may flower and die no mater what you do. But like many generalizations, this does not always hold. Phyllostachys elegans at The Bamboo Garden has flowered sporadically every year for about 10 years while continuing to grow with moderate vigor. It, has not been restored to a vegetative, non-flowering state, by our prune and divide strategy. It continues to flower and grow with no sign of stopping.
Some species of bamboo seem to have a few plants in flower somewhere most of the time.
In China there always seem to be some Moso plants flowering. Growing from seed is exciting. It however, is not the way to save a flowering bamboo clone with variegated leaves or yellow or striped culms. These and other special clones are best saved vegetatively if possible. The seedlings will most likely return to the original type.