When exporting a batch of images, there is at least one warning condition — ambiguous modules — which can be bypassed to allow the export to run.
However, if an image specifies a watermark image that cannot be found, that image causes a hard error and is not exported.
It should be possible to allow that hard error to be a warning and export without the watermark.
Alternatively, a mechanism for locating missing watermarks would be useful. At some point in the past my watermark file moved location, likely during a computer migration, and now I have a lot of old photos that refer to the wrong location and this is very difficult to spot if just re-exporting.