Even if it doesn't pop off the bed, as the top layers cool they contract (especially noticeable on the larger pieces which require long print times). Even if you bookmarked the layer, did a Z move to get the head away and came back clean the next day, that shrinkage would leave you with a dirty great step in the print. You'd also have layer adhesion issues trying to print onto a cold last layer.

If you aren't set up to run lights out, you have three options I can see:
1. Set up for lights out running. Wire a smoke detector above the printer to a cutout relay to its mains power or something and a CO2 fire extinguisher like that so, in case of meltdown, it shuts down and puts itself out. Doing this right = hard.

2. Move the printer to where you can keep an eye or ear on it for the whole job. Take it home, set it up near a smoke alarm, do other things and let it keep running but don't get out of earshot.

3. Break your print job into components with some interlocking mechanism, where each component can be printed within your window. Dovetails, jigsaw interlocks, using bolts or screws, even glue. There are many options for doing this.