What is the difference between copy number changes with and without allelic imbalance?
Allelic imbalance is a pretty broad phenomenon difference in the expression of two alleles.  As such you have listed would probably cause allelic imbalance, but it could be the result of methylation or even differences in RNA sequences between the alleles which say interfere with post translational splicing say. 

In the case of copy number variations, if a copy number region (which is often a higly repetitive sequence in the genome and not a gene duplication) might interfere or not interfere with gene regulation. In cancer cells large segments of the genome may be copied or cut out though, so in that case the mechanism you put forth may be important.