is there a tool with which I could have gotten back a readable sketch from it?
Not possible. What resides in the chip is the AVR machine language instructions from the output of the Gcc compiler. The original sketch source text only resides on your PC. Trying to read back and take the machine language instructions, reassemble it to assembly code text and then try and convert it back to C/C++ source code is nearly impossible for all practical purposes. Even if possible by some experts there would be no way it would include your original source comments nor the names you used for variables and functions you created in the sketch.