This is a special moment that most people who use 3D printers know very well. When you check the printing for 13 hours, you find that the printing failed hundreds of layers ago. [Stephan] of [CNC kitchen] has some clever tricks to recover failed printing.
It starts when you find that printing fails and whether the part is still attached to the bed. If it has fallen off, the best thing you can do is take out your caliper to get a fairly accurate measurement of how much is printed. Then cut off the printed part, print the remaining part, and stick the two parts together. If your part is connected to the printing bed and you haven’t moved the plate (if it’s removable), start by removing any defects on the top layer. This will make it smooth and predictable when starting a new print based on the existing print. Measuring the printed height is tricky because you can’t remove it. Calipers long enough can use their depth function, but visual inspection can also be carried out if the geometry is unique enough. After loading the model in the G code viewer, browse layer by layer until you find something that matches the printed content.
The last (and perhaps smartest) way is to use the printer as a temporary CMM (coordinate measuring machine). Manually step the printer until it touches the top of the part, and then read the z-axis height through the screen or M114 command. A quick edit of the original G code will provide you with a new file that will accurately restore the previous operation. If the head cannot be relocated because it cannot clean the parts, Stephan will guide you to manually set the origin of the printer.
If all this doesn’t work and the print still can’t be recovered, maybe you can consider recycling the plastic into a new filament.