People used rifles (and shotguns) for over one hundred years without magnified optics and got along just fine.
It is interesting to look at some old issues of gun magazines and see what used to be considered a long range big game rifle.
Yes, you can get along fine without a scope. I grew up in Ohio and still go back there at least once every other year to hunt whitetail deer and up until last year, I had never used a scope.
A scope provides you with a couple advantages: it puts everything on one focal plane. With iron sights, the target, the front sight, and the rear sight are all at different distances from your eye. Your eye can only focus at one distance, so the correct thing to do is to focus on the front sight and allow the rear sight, and the target to be blurry. With a scope, everything appears to your eye as being the same distance from your eye. This makes things a little easier. Second, the scope makes it easier to see in poor light. Third of course is the magnification. One note about magnification: DO NOT use your rifle or shotgun scope as a binocular. Do not use a rifle scope to see if that object over there is in fact a deer etc. This is a violation of the basic safety rules of gun handling: Do not point your weapon at anything you are not willing to kill. That movement, or that object you spotted just might be another hunter. Whether or not you decide to put a scope on your shotgun, use binoculars for spotting. I have been on the recieving end of this and it is VERY unsettling. I saw another hunter walking through the woods while I was sitting on the ground. I waved to make sure he saw me and realized I was a human. He raised his rifle and looked at me through the scope. Time slowed way down as I wondered if he was going to shoot me. I have decided that if this happens to me again, I am going to walk over to the guy and punch him as hard as I can, right in the nose. If safety isn't reason enough not to do this, it is also illegal to point a loaded gun at another person unless you are defending your life.