When photos are missing during publish & export, give the option to locate them, much more helpful than saying some are missing and would you like to use a low quality image / thumbnail or cancel...
Might be more helpful to have a nice warning box show up, say as a row at top of screen, just below menu bar, show that some images are missing. Would be easier to notice than looking at ? or ! in Folder panel and/or grid, etc.
Would be even better, if you could click on the warning to fix.
It could be added to the publish folder plugin, by Fredi I think, just needs an option to check for missing photos before publishing and offer the option to locate them.....will suggest it, maybe you never know