The most likely outcome for the panda species, given that their primary diet consists of bamboo and they have a slow reproduction rate, is:
The species will become extinct since it cannot adapt to the changes fast enough.
Pandas are highly specialized feeders relying almost exclusively on bamboo, and without it, they do not have the ability to quickly adapt to new food sources or find alternative habitats. Their slow reproduction rate further compounds the difficulty in recovering from such an environmental catastrophe.