What is the life expectancy of adult who had a transposition of the great arteries surgery?

Generally good. An adult likely underwent a senning or mustard procedure (atrial switch operation) for tga. The 20 year survival is reported to be about 90%, but many patients have abnormal heart rhythms and some have abnormal heart function. This group of patients has a reduced life expectancy, estimated by some to be 45-50 years (63 years after an arterial switch operation).
Perhaps normal. The current surgery for transposition, the "arterial switch" was not common 25 years ago. So far most patients do very well, although there are a few potential problems which may occur over the years. We are hopeful that the life expectancy for most of these patients will be relatively normal. Time will tell. Prior to the arterial switch procedure life expectancy was notably decreased.
Transpositation. If the transpositation was corrected completely then the individual should have a normal life expectancy. Ther is the possibility of that person having rhythm disturbances or arrhythmias of the heart. However, these are not usually life threatening.