The most likely outcome of the reduction in the bee population due to an increase in the population of a bee predator (such as dragonflies) is:
The plant community will become smaller and less diverse.
This is because many plants rely specifically on bees for pollination. If bee populations decline significantly, these plants may fail to reproduce effectively, leading to a reduction in plant numbers and diversity. While it's possible that other pollinators might emerge, the immediate and most significant effect is the impact on the plants that depend specifically on bees.