Ok what can be done about moderate towards sever ligament damage (triquetral ligament) ?

Depends: I don't treat x-rays or mris. I treat pain. If the pain does not resolve with simple measures then more complex surgery is recommended. We know from the fact that some people are born with the lt bones fused that the loss of motion from an lt fusion is minimal.

Need more info: First thing is to confirm the diagnosis. Second, establish what symptoms relate to this. Speaking very generally, if symptoms are minimal would try immobilization. If there is some degree of instability would need to investigate further. Carpal ligamentous injuries can be very tricky to treat surgically.