It is highly unlikely, however that is just what happened to me 5 yrs. after I had my tubal ligation. Failure rates are around .1% or 1 in 1000. Tubal reversal surgeries can restore your fertility after tubal ligation in about 75% of cases.
I had my tubal ligation done on January this year and I become pregnant six months after the surgery, i still not believe it, i was in shock when I got the good news, but it happened to me, so it can happen.