Jesse,
Don't panic, take a deep breath first.
Firstly, I assume you're using the latest version, Xmind 7.5 update 1 because you don't state other.
Test your installation. Make a new map and add an image to it, i.e. copy an image to the map. Save and close, reopen Xmind and the map. Is the image still there? If not, your installation has somehow got corrupted, reinstall Xmind.
Make a copy of your "disappeared pictures" map. Continue with this copy. DO NOT CONTINUE WORKING WITH THE ORIGINAL IN ANYWAY. Does the copy open? Does it contain the images? Do you have a backup of your map somewhere ,say, in a cloud storage service (Dropbox, Evernote, Google drive, Icloud, OneDrive etc.)? Are there any previous versions in Editing History in Xmind? Go back version by version, begin with the second-to-last. Can you recover your map?
Finally, if none of these help, contact Xmind's support directly, see
If they ask you to send your map, send the original.
HTH