How to recover deleted photo when recently deleted album is missing on iPhone?

When you delete a photo, it goes to the Recently Deleted folder, where it remains for up to 30 days to give you the opportunity to restore if you want. If the photos were deleted more than 30 days ago, they were automatically removed and if not backed up anywhere else, they are gone.

Are your pictures maybe still in the Library? Albums don't actually "contain" pictures-- they are just lists of pictures you want to see together. So deleting an Album, deleting the list, doesn't delete any pictures. (But the Album list is gone forever.) So, if what you did was just delete an album, then the pictures are still in the Library.