This is what happens with every one of these check valves that I've ever seen. A while ago, the return pump failed on one of our displays at the National Aquarium and I was working on replacing the pump. Suddenly, the sump started overflowing. I shut the valve on the return line and tried to figure out why that happened. Turns out there was a check valve on the return line, and it was the only thing stopping gallons of water from draining into the sump and flooding the backup area. And shocking, the check valve failed.
If your sump overflows without the check valve, I promise that your sump will flood at least once because the check valve does not close you expect it to. I personally would never plumb a system so that a check valve is needed to stop the sump from overflowing.