Files within a specific collection deleted from hard drive

About 1 year ago I created a collection of about 200 of my favorite photos for the purpose of choosing 25-30 for a print project. The collection was synced with LR. These were all photos from my LRC catalogue, residing on my local hard drive. Last week I started to export some of my photos for printing, and discovered that about 50 files were missing, although the smart preview and xmp files were still present. I tried to locate them in the parent folder and could not see them. When I tried to locate the files with the LRC finder I was directed to the Mobile downloads lr folder, which they were not in. I tried to manually locate these files in their original folders on my hard drive and searched my entire computer with the help of an IT person and could not find them anywhere. I use a cloud based backup (dropbox) and searched with the help of a representative and could not locate them in any deleted files folder. The vase majority of these files were photos I had brought into PS and saved back into LRC as TIFF files. Not all TIFF files in the collection were missing, although the majority were. I also searched my LR program and could not locate them there. 

So, I am at the point of hiring a recovery service to try to salvage them from my hard drive. Curious if anyone has heard of this, any help or guidance would be appreciated. Thanks.