I firmly believe that the hyenas weren't evil in and of themselves. They were in a bad situation, bitter and longing for food, just like any marginalized group. The thing is we do not know who started the conflict between the lions and the hyenas, and probably, by the time of the events in the film, they didn't know either. But if you watch the "Be Prepared" sequence, you can see that the hyenas never would have actually considered killing Mufasa on their own. They were surprised when Scar suggested it. They didn't like lions, sure, but they weren't truly evil. They were Scar's lackeys and that's the only reason they committed evil acts, because he promised them food and prosperity if they did.
So, if Scar was not evil to put the idea into their heads, they would probably have continued living the way they were for a while before eventually doing what they did between the movies; leaving. Mufasa would not have been killed, the stampede wouldn't have happened. Simba would not have met Timon and Pumbaa. Scar probably would have had a mate and/or cubs. The events of SP never would have happened. Kovu, Vitani, and Nuka may never have even been born. The drought that occurred during Scar's reign canonically probably would have been much easier to survive without hyenas drinking all the water and eating all the food (hyena clans irl can be up to like 80 individuals, if I remember right, so that's a lot of food and water). Things as a whole would have been better.
Of course, for that matter, everything could have been different. For all we know, if Scar hadn't been evil, he and Sarabi might have gotten together, and maybe Simba wouldn't even exist.