I don't think the US would stop trading with Puerto Rico, so I suppose the question is if the increased trade with Caribbean nations would offset however much trade with the US mainland would diminish. I don't know the answer to that, but it could probably be found by looking at how Caribbean nations' trade compares with Puerto Rico's trade today.
Yes, I'd just expect the "common market" effect would be significant. I'll bet it would have been harder to manufacture pharmaceuticals for sale in the US in the Dominican Republic, for instance.