Why can't the electrophile attack the chlorine atom in a halobenzene?
Given the charge distribution and the shape of the HOMO, I would be very surprised if an electrophile does not attack the chlorine. This is from a calculation on the DF-BP86/def2SVP level of theory.

If you account for the hydrogens effectively shielding the negative charges of the carbons, the only place left to go is the chlorine. (Natural Population Analysis, NBO 6.0)



The largest coefficient of the HOMO is at the chlorine (C1 ipso, C4 para):

Alpha occ 29 OE=-0.224 is Cl12-p=0.29 C4-p=0.24 C1-p=0.19 C2-p=0.09 C6-p=0.09




Generally I would expect it to be rather unreactive towards electrophiles.