I haven't had a rear sway bar in years and have had no ill affects. I drive on the expressway every week and being lifted on 33" tires in a vehicle with zero aerodynamics, you're going to get pushed around by the wind regardless. Definitely no flex benefits without one though.
I have run no rear sway bar for about a year now. The reason that I removed it was because of some back yard wheeling. I was attempting to climb a stump with the front discoed and rear bar connected. I wasn't able to get my jeep up the stump because the rear came off the ground just enough to spin and stop forward movement. I then removed the rear sway bar as well as disco-ing the front. Once I did this I was able to climb the same stump without the tires coming off the ground. Now it's possible it was all just luck that I climbed it fine without the rear sway bar, but I tend to think it is more because the sway bar was off. All that to say I haven't been running one since and it's somewhat noticeable on the street, but nothing life threatening; it just means you can't corner like a sports car
95 FiveTwo ZJ, DD, Lifted, Locked on 35s, Build (in progress)