In the past I have done a few hacks...one was to remove all methods from the class and only implement #doesNotUnderstand: calling the deprecation method saying the class was deprecated and now you should use xxxx.
In another case, I didn't want to remove methods from the class for some other reason, so if I remember correct I hacked it but doing a Smalltalk at: #MyClass put: ��self createDeprecatedClass.
And #createDeprecatedClass would create a dummy class with no method but the mentioned dnu...
But for sure we need a better way to deprecate classes and packages too!