Per code all copper joints underground are to be silver soldered. If it has not been properly soldered it does not mean it will fail. It probably will not pass inspection. I personally do not think you are taking a chance leaving it as is. Good Luck, Bill The Local Plumber Tustin, California http://www.TheLocalPlumber.com
For everyones info, the pipe is under dirt and sand, not directly under concrete. By the way what is the difference between brazing and soldering. Will it make that big of a diff in my case. The plumber I use is very good at sweating/soldering copper. Should I leave it?