“Can hand nerve damage from a stroke be repaired?”

I am sorry your friend has had a stroke causing some problems with his or her hand.  There is no way to "repair" nerves damaged by strokes, but with time, some patients do recover some or most of the function in an area damaged by the stroke.  PT is very helpful, and your friend needs to do whatever is needed to prevent additional strokes, which might be medications.

In stroke, there are damages to the brain cells (neurons) of the affected sites, more motor than sensory. It often causes partial paralysis of the upper extremity, distal (hand) more than proximal (shoulder). There is no nerve damage to the nerves of the hand, in fact, no damages to any peripheral nerves anywhere in the body. Its recovery largely depends on recovery of the damaged brain cells, nothing to do with peripheral nerves in the hand. Not much can be done to enhance its recovery.   

It is only possible and depends on the type of damage, the age and health of the person, and how bad the damage is. In looking at rehabilitating, repairing, or regenerating nerves, the word "damage" does not tell us enough to give a more detailed answer.