^Well, in the first movie, the wildebeest herd are seen grazing in a field of fresh green grass, which makes me believe there is a water resource somewhere to maintain the grass to look healthy.
Actually, I tend to believe 1.5 waterfall is where the hyenas found the wildebeest herd, and where the stampede started from. Remember, after Timon and Pumbaa fall into the stream of the waterfall, you can see the wildebeests grazing in the background which leads me to believe that's where Simba's stampede started from. Here's a screenshot below to prove my point:

As for the "revived" topic, not necessarily. Timon and Pumbaa must have traveled a distance depending on where the current of the plunge pool pushed them. Where exactly that direction took them is unknown.