I'll post debug, sure. But, as you noted, it's when the device isn't connected, wrong device selected or the device just doesn't respond correctly. In IDE v1 when you unplugged the device avrdude would quickly die. Now, even when closing the window for that specific sketch, avrdude continues to run in the background and eventually uses a bunch of CPU and I have to manually kill it. A new window will work fine for the sketch to upload, so not sure what avrdude is doing.
I don't know why there isn't a "cancel" button for this, just kill the avrdude process and let's move on. There are many reasons why the upload will fail, not being able to resolve that in some tactful way for the user seems like the issue.