Please go into a little more detail. Are you saying that the rest of the site stops working for Image handler? or are you saying that the image on the product info page doesn't zoom?
If it is the latter, please note that the image on the product info page never zoomed. It is considered the "large" image which doesn't have a zoom option.
You can see IH2 still works on the sideboxes and main page and stuff on my demo site that has TPP.
DEMO
To test further, you can remove the product display info overrides in your template folder and use the one that is in template default and see that it also does not zoom.
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