I guess it depends on how far the flashing process got. You may have borked your recovery partition at which point you'll have to put it into download mode and reflash the stock firmware. Getting it into download mode might be a bit tricky. To put an S6 into download mode (odin mode) you press the vol. down, power and home all at the same time. Since you are already pressing the vol. down and power button for the simulated battery pull, and it reboots immediately after that you may have only a second or two to press the home key too. It might take a couple of tries and it might be that the instant the screen goes black, you have to release the buttons and re-press all three. (But first, I'd just try keeping vol. down and power pressed and then pressing the home button when the screen goes black.)
If you can get there, then you can flash the factory firmware. You'll of course need to get the right version from sammobile.com and have the right version of odin.