One of those things you just never know about. Leaks may stop after time because minerals build up and clog the leak, or corrosion in iron pipes. Me, I'd not sleep at night knowing a pipe is not properly soldered and could get worse while I'm away on vacation.
At work we had a joint not properly soldered in a 2" copper tubing. It never leaked, but the tubing was not properly seated into the elbow. It took about 8 years, but if finally let go one morning. Thousands of gallons of water flowed before it could be shut off.
I'm not familiar with the tape, but I'd not trust it. OK for an emergency, but I'd still fix the pipe properly.