This may not be correct, but it is the best I can come up with.
Another possibility would be to connect the two sentences as if they were one. But that would be indistinguishable from the single compund sentence diagram, which wouldn't be completely accurate. That said, this is an issue of punctuation and punctuation is really not considered in diagrams. If you choose this model, you would diagram the two independent clauses on separarte main lines, one over the other, and connect the verbs with a vertical dotted line connecting the two verbs. The conjunction would be written sideways on that dotted line.