It can be repaired, but there are a couple questions one must ask, are you the one that can do it? Do you have the tools to do it? Do you possess the knowledge to do it right? Then the big one, will the customer be ok if it doesn't go well?
One will never know if they possess the knowledge and ability if they never try, I say go for it, as long as the customer is ok with the potential results, good or bad. It will be a learning experience that cannot be learned from a book or video. It will test your abilities, and knowledge, and ability to deal with a customer if things don't go well. My advice is make sure they are willing to put a deposit on the cost of materials upfront so you don't get f@$ked. It will be as expensive to repair as buying a new cue, and you will need to do a new wrap....not easy if you haven't done one before. BUT, considering the customer DESTROYED this cue without a second thought......They should feel privileged that you choose to help them,....for a cost. Make sure you cover costs and some profit.
The first forearm I ever built and installed was on a buddies 20 + year old Viking that he snapped the forearm over his knee. It was a Mahogany forearm, and he Broke it just above the A joint. I replaced it with a similar piece of mahogany, but it was cored with a laminated dowel, and I went about 5" into the handle with the laminated core. I have told him since, he tries it again, he may break his knee cap before the wood lets go...he hasn't done the same thing again. Been about 9 years.
I will say, I am amazed at people that will break their cue in the heat of things, but then want it all be put back together because they REALLY LIKE THIS CUE.....wtf.....I just don't understand it..lol
Dave