I would try closing the valve. If it works, test by using the sink until water starts to rise somewhere. Then open the valve, and expect the water to recede. I think there is a very good chance it will work. Whoever installed that was motivated. You don't want to wait to get similarly motivated. Gate valves seem robust to me, but I am not speaking from experience.
If this works, it could be worth keeping and working around. If practical, put an alarm at the spot the water rose during your test. If that is a floor drain, then that is easy . When you hear the alarm, close the valve.
Make friends with a neighbor or 2 downhill, and ask them to phone you if there is ever a sewer backup.
Avoiding other people's sewage backing up is good. Doing it without a first hand negative experience is better.
If you want to replace the , you would dig the area up. Put in a vented sewage pit with a grinder pump, and let he basement pipe only empty into the pit. Pump the sewage up to basement ceiling and join the plumbing there. Alternatively, have the sewage go through a new hole maybe 4 feet up in the basement wall, and have that sewage join the sewer line outside. If you do that and pipe all upstairs sewers to be gravity feed via the higher exit point, you would have the classic "overhead sewers". That is the best way to deal with sewers that occasionally back up.
Your city might contribute significantly toward overhead sewer installation.