If they tried with a large enough object I wonder if they could film it going through the slits, like with a high-speed camera. I guess individual molecules can't be photographed without an electron microscope though.
Observing the object in either one of the slits would remove the necessary precondition for getting the interference pattern on the wall, so the pattern would no longer be there in your experiment.
If you observe it before passing, if that's possible, the wavefunction will collapse at that moment, and the quantum will pass, like a particle, through a single slit.
No idea how it would be possible to observe it mid-flight though.
...according to the most commonly accepted interpretation at any rate.
Well, as soon as you "observe" it, we will no longer see an interference pattern
That's not strictly true, because the experiment is observing the quantum, and it is seeing an interference pattern. The critical thing is that they're observing it after the quantum has gone through the slits, so as it passes through the slotted wall, it's wavefunction is not constrained. So the moment of observation is very important.