Aviation Insurance claims repairs have to be completed in the most cost-effective manner. The use of OEM repair teams normally adds a significant cost to repairs and engineering teams will often go down this route and then when the bill comes (which often ends up in another department dealing with Insurers) it will get assessed on that basis and Insurers may not agree to pay the full amount if there was a more cost-effective option.
Rationalfunctions is correct, two possibilities if no agreement between parties exists then liability will probably be unlimited against the ground handler. If there is a standard ground handling agreement in place between the operator and ground handler then certain limits of liability will apply.
Whilst the damage looks bad it looks like it has missed the trailing edge wing spar. The raked wingtip can be replaced as can the trailing edge panels. Probably the biggest part of the job will be the replacement of the wing tip closeout rib which can be seen bent inwards in some of the pictures online.