Well, assuming that you used arctic alumina epoxy, you can get it apart. I've potted small converters in this stuff and had to dig through it to change sense resistors. Really, if you heat it up in a controlled environment, like a toaster oven to about 170*F, the arctic alumina gets gummy and you can actually separate parts and remove the epoxy with an exacto knife.

If you use an oven to do this, be sure to preheat it for about 20 minutes or so before putting in the esc. Ovens tend to spike the heat to quickly attain the desired temp, before settling on the set temp. The hotter you go, the more gummy the epoxy gets. Just don't melt the esc.