I suppose you could take it off the bed, measure very precisely the height, print just the remainder (by altering the model and re-slicing) on the bed, and glue it to what's already printed. It would almost definitely still have a visible seam and aside from that, I can't think of a way to save it.

Do you have a pair of calipers that you can use to measure print height? If yes, don't take it off the bed. Measure the height of the print, delete those layers out of the gcode (it's just a text document after all), and reset. Note that the gcode and printer setup might require some fiddling to get right, but I've resumed prints like this without problems before. They don't all look perfect at this layer, but they're certain better than nothing. Once the print loses its hold on the bed, all bets are off.

Instead of using a caliper, like the others have said, you can measure the distance with your printer if you don't have such a tool.

Just go into the "Move axis"-mode, and move your nozzle from the home position to the top layer.

Let's say your coordinates are now X0, Y0 and Z49,3.

You can then move the object in your slicer by just changing your Z axis to -49,3.

Just make sure you:

1. Get a good first layer, without getting an elephant's foot.
2. Don't use too much glue. A good choice is acrylic glue, but it will alter the surface if it droops out or is too far outside.
3. Don't mechanically stress the object too much. It won't be as strong as before.