It can can be converted to a full sized wav, but not restored to full quality.
The MP3 conversion process discards some information as part of its compression scheme. This is called "lossy" compression.
Other types, like FLAC and AAC Lossless can be restored to a full quality WAV as these are simply bit compression methods, like .zip or .rar. These methods are simply "unzipped" on the fly to play back as if they were an uncompressed file.