pay off 是回报,起效果的意思。
He 是主语
says 是谓语
that decision is paying off in better health for their people 是that引导的宾语从句;
is paying off 是现在分词,意思是正在起作用;
in better health for their people 是状语,在给人们更好的医疗条件方面;
连起来就是,他说,这一决定在改善医疗服务上正在见效。
pay off 可以理解为回报
所以,那个决定已经在改善健康上开始回报了,也就是见成效了。
另外,这里that不是从句,而是修饰decision的,指“那个”,真正的that被省略了,实际应该是
He says that that decision...