Etiquette question: Do I send a wedding gift if I can't go to the wedding?

A (not very close) friend’s son is getting married at a distance. I had told my friend that we wouldn’t be able to come. There was an engagment party locally at which we did give a gift jointly with my son who is going to the wedding. Should I send a check with my RSVP or was I covered by the engagement present? I want to do the right thing.