I see your point and i like the way you describe the facts. But I don't see all this big problem going on. First of all, we'll have del piero for another season, so for the upcoming year, we're covered (even though it seems he can't play his full 90 minutes anymore, c.f. NT).
As for replacing the 'bandiera' del piero, it's sure that it will be hard, but someone like buffon can make a good captain too imo. I agree that except buffon, there might be a small gap, but until then, there's plenty of time for a new bandiera to come up (giovinco maybe, chiellini, ...) We all know that someone like del piero can never be replaced and that the footsteps our beloved captain leaves behind are impossible to fill, BUT, there are some candidates going on that could do the job...
If you are talking about replacing del piero on the pitch, i think we're on a good way too. We signed amauri (which i rate pretty similar too del piero, maybe a little more attacking) who will go on for some years, and then we'll have plenty of options; palladino, lanzafame ... or if they don't fit the expectations we can still aim for a big buy (because until then, we'll have settled in CL too probably)
It's cristal-clear that Alex cannot be replaced; neither on nor off the pitch. But i think we are at least doing our best to do so. I don't see what we could have done better up until now.
Back to the cassano-subject; people considering him as underrated are wrong in my opinion (this is just MY OWN opinion) In fact i believe he's pretty overrated. He had some excellent games, but a complete player has more than that. He has been given lots of chances to shine, and he always failed because his personality just let him down. It's useless talking about him as the poor chap who is soooo talented but desperately tries to improve his attitude. That's just wrong because it seems to me that he does not WANT to change, and this makes him pretty much worthless in my opinion. I won't ever question his footballing skills, but i'd prefer someone serious, willing to give everything to improve over cassano any time. as said, this is my opinion...