Accidentally deleted a batch of photos from my computer completely; however, they STILL are on my Lightroom. The only thing is - it says "photo is missing." Is there any way I can restore these photos from Lightroom?
Your photos were never "in" Lightroom. Your photos were just files on your hard drive, and LR knew how to find them by path and file name.
What LR can show you without the actual files are the previews of the files from inside the LRDATA folder.
Check your "recycle bin" or "trash can" to see if your photos can be undeleted. If not, check your photo backups to see if you can copy them from there. If not, they are really gone.