Q: Worn ball joints causing excessive tire ware.

Took my truck to the local Ford dealership to have an emission problem repaired. While in the shop I decided to have a tire rotation and alignment performed. I was told that the ball joints are worn out. My service representative recommended that I not have the alignment performed as it would be out of tolerance again within a week. Addintionally, he advised against replacing the ball joints reasoning that this repair would need to be done again in a couple of years, and given the expense of the repair, compared to the cost of new tires, would not payout. Needless to say, I left the dealership without having the ball joints repaired and puzzled about alignments, tire ware and buying a new set of tires.

My question to you is: how long should I expect repaired ball joints to last on my truck. 99% highway/ paved road driving, lite loads, conservative driving habits.

My car has 155000 miles.
My car has an automatic transmission.