Any professional artist should seriously consider having their work insured under an insurance policy specifically designed for artists.  As well as the specialist insurers listed on Artquest, both a-n and the Society for All Artists provide insurance policies for their members.

If an offer of restoration of the work is made, and you agree to undertake the restoration work yourself, you should write to the insurers setting out the costs involved for your time and materials.  If an independent restorer undertakes the work, care should be taken that you are satisfied with the restoration. As an artist you will be concerned that your moral rights are not infringed by the work being so badly restored that it becomes the subject of derogatory treatment.

If the dealer intends to have the work restored you must make it clear that if you are not satisfied with the restoration, then you reserve your right to disclaim authorship of the work and have wording proclaiming this permanently attached to the work. This would confirm the date that the work was created, the dates of damage and restoration, and that as it has been restored without your consent or approval you no longer consider it to be your work.

It is also worth noting that whilst defacement of your work would infringe your moral rights, destruction of it will not.