Answer:
The impala population will decrease.
Step-by-step explanation:
We learn that leopards eat both baboons and impalas. If one of these two species is reduced in abundance, the leopards will increase consumption of the alternative, in this case impalas. An analogy: If you eat only chicken and beef, and the local store ran out of chicken, you'd choose beef, as everyone else in the same predicament. The leopards see fewer baboons because of the disease, so they'll start hunting more impalas, and the impala population will decrease.