There's more to this story. What I think happened is the engine was losing a bearing or two and it may have wiped the front out which caused the balancer to go ****eyed.

 

Harmonic balancer failure by itself is fully recoverable, with a replacement and maybe a belt. If you got some crank walk or something as the real root cause, then your guy is probably right. Doing major repairs on the bottom end might not make sense. You're doing the right things to ask some more questions.

 

See if it's possible to have someone weld a new balancer to the crankshaft snout. You have nothing to lose at this point and it might last for another 100,000 miles like that.

 

This seems like a terrible idea. Why would you suggest this? How would you get it apart if engine work was needed?

 

Obviously it would not be able to be removed, but throwing away a 56,000 mile motor and spending $1000's of dollars when a few hundred dollar weld job might save it and then he could drive it until the timing chain needs replacement. It's just an option that the OP might not have thought of.

 

I still think just a new balancer and crankshaft bolt should fix the problem, but photos are required to confirm