I think you already answered your question regarding the force, since you explicitly stated it.
However, if I'm understanding you correctly, I think you might be getting at the concept of linearity and the superposition of fields. Is your question what the resulting field would be if it varied as the square of the sum of all the masses/charges in some way? If so, you likely could not use Gauss's law at all, since it's a sum which assumes that the total field can be produced by summing each up piece of field, which in turn assumes a sum over each charge/mass. If the field produced by each infinitesimal source cannot be added linearly to produce the net overall field (that is, it is not independent of the other charges/masses present), then this sum does not give you the total flux, and therefore cannot give you the total mass/charge. In other words, by summing the field, you are no longer summing the total charge/mass, since they are not linearly related.
To answer your original question, if the divergence of the electric field were proportional to the square of charge, then nothing would really change other than we'd probably treat the fundamental charge as its squared counterpart (and some units would need to be added or modified). It would still be linear in superposition, though.
(Note: This is intuitive reasoning. Correctness not guaranteed.)