Oh my lard, Mandy! My heart stopped for a brief second as I read your story, and I am fighting back tears at the moment. That is so upsetting!
When my daughter was 4, we briefly lost her near the Haunted Mansion at night. I thought that DH had her. He didn't realize that he was supposed to "have her" and therefore wasn't paying attention to the toddler following him. When we realized she was missing, I nearly lost my mind. There were thick swarms of people everywhere (making it nearly impossible to see persons low to the ground); it was dark; no CMs in sight. I was SCREAMING her name at the top of my lungs. We located her within 3 minutes, but they were the longest 3 minutes of my life. If I had found a suspicious man carrying her off . . . I surely would have had a nervous breakdown.
Everyone else has good advice about trying to not let this rule your life, but having experienced a more mild version of your nightmare, I can understand why your vacation ended and why you may need a break from WDW. I may be neurotic about my love for Disney, but it is nothing compared with how neurotic I am about my love and protection of my family. Please give your precious daughter an extra hug and kiss from me. I am so glad that she is safely with you. And I do hope that you find you are able to eventually return to WDW.