I love Arpege pour Homme, and I am really hopeful that it won't disappear. Anyone who likes/loves Arpege should find Cadillac for Men by Cadillac (2009) to be an acceptable substitute. I have done side by side, day long comparisons of these two, and I find them to be very similar. The differences I noticed are that while Arpege PH features a prominent Iris note, Cadillac has a dominant Tarragon note instead. Arpege has better longevity, but not by much. I own Cadillac EDT, but it also comes in an EDP for those concerned with longevity issues.
There really isn't a substitute for as lovely a fragrance as Arpege pour Homme, but I offer the Cadillac suggestion not to hijack the thread, but to offer some hope and an alternative for those of you (including me) who really love Arpege.