Once you open a can of sauerkraut the opened can of sauerkraut will last for up to 7 days in the refrigerator.
If you want to keep the opened can of sauerkraut longer than 7 days you should put the canned sauerkraut into a freezer safe container and freeze it.
Frozen sauerkraut will last for 6 months to a year but for best taste eat the sauerkraut within 6 months as the longer it's in the freezer the less fresh it is.
It's still safe to eat past those 6 months but it won't taste as good.
Also when you refrigerate the canned sauerkraut make sure to seal it with something such as a plastic wrap with a rubber band to keep other smells from the refrigerator from getting into the sauerkraut.