Should we remove the attachments info when not copying resources?

In the image select question, when not copying, the broken link remains.
When linking a file in the welcome message and not copying the message, the broken link remains.
So, should we clear the attachments for emails?

What if we:

• Add a warning on the email screens saying some attachments are not valid.
• Highlight or mark the attachments which are not valid.
• Add a message when copying saying some attachments are not valid anymore as resources where not copied.

As for the possible broken links on image selects or other texts in the survey:

• Add a message when copying saying some links should be reviewed as resources where not copied.
  (For another ticket).

Still, right now, non valid attachments are not attached, so, keeping the non valid attachments doesn't harm.

Not sure if this is worth of tacling this at this time.

These suggestions sound fine to me.

Waiting for 18557 to be merged before pushing the solution into a PR
https://github.com/LimeSurvey/LimeSurvey/tree/bug/18602--Email-Template-Attachments-appear-to-carry-over-with-copied-survey--but-do-not-work-2