It won't hurt anything usually......but to avoid chassis lean and keep the car cornering better, both sides should be connected.

An easy way to fix it is to buy the long bolts/nuts/washers and rubber bushings located at the ends of the sway bar from Pep Boys or the place of your choice, and replace both sides. Sometimes the replacement kit includes a new bolt, sometimes just new rubber.

Look at how the "still connected side" is arranged from top to bottom (nuts/washers/rubber, etc.) on the long bolt, and duplicate that order
on the un-connected side. Then duplicate what you just did on the connected side.

That way you get new rubber on both sides of the bar ends, as well as fresh un-rusted hardware, making your next replacement easier. I prefer nylock-type nuts or a drop of locktite to keep nuts from working loose.

Your ride/handling will be better, the cornering will be better, and the newer parts will last longer.-Bob