Can you duplicate the crash on any patch with missing samples or just a certain patch? For instance, if you go to a very simple, basic Kontakt patch and rename or move one of the samples it uses before loading it, do you get the crash as well? Does it crash Cubase? (seems like it would usually as Kontakt would be running in its process)
Do you have a copy of the patch outside of Cubase? If so, can you load it stand-alone? If you get the find sample dialog there, it might be possible to move the samples to where the Cubase-saved patch can find them without searching and get your project opened that way.