Most definitely can go back. Same with AIFF (Apple version of WAV). Lossless is simple data compression. FLAC, ALAC, APE do it in their own ways but the data is the same. Lossy MP3, AAC, etc. are conversion schemes that take away some (a lot) of the data in their attempts to retain the sound in the data they keep. Since they take away data and and the data that results is not the same (not the same bits) you can't recreate the original, nor can you go to more or less bitrates. The latter is the second reason for archiving as lossless. At any given moment you may find yourself wanting a lossy version, say to load up your phone/player for a a trip where you will not be able to stream. Say you decide you had done smaller/larger files (lower or higher bitrates). Using lossless as the original file your golden. But if your archive is only whatever bitrate you originally encoded to you're screwed. This is why I cringe whenever someone brags about ripping their entire collection to 320 or whatever.
Sorry, most of that wasn't directly related to your question. Just killing time.