In a single slit diffraction experiment what would happen if the slit width is reduced to almost zero and if we are also watching the electrons with a light source. Will it still show a fanned out diffraction pattern or will it have a narrow concentration in front of the slit just like if it was like a particle?
It depends on the wavelength of the light. If the wavelength is significantly smaller than the width of the slit, then the scattering of the light would smear out the diffraction pattern and it would look like a single bright band in the center. On the other hand, if the wavelength is comparable to or larger than the size of the slit, then the influence of the scattered light on the electron will be small enough that the diffraction pattern might still be resolved.
It's worth noting that if you're going to use electrons in the experiment, the slit width would have to be exceedingly small - much smaller than the slits in the elementary lab equipment that you'd find in a first year physics course.