Disband them once our pikemen are finnished. They hamper production and are of no use to us.
We will probably not get Leo´s very soon, and when we do pikemen/musketmen are cheap to build. The resources we save by upgrading phalanxes through Leo´s will not by a longshot upweight shield-loss until we get it.
Btw, I think Leo´s is to be downpriorited. Lots of wonders will benefit us more, like Magellans, Copernicus, Bachs, etc. Our cities are desperatly lacking production, so we can´t build all of them.