For my money I think Twitter is more dependent on third parties than third parties are on Twitter. Not just Instagram, but the entire ecosystem of apps that grew up around Twitter in the bygone days of warm fuzzies.
Twitter seems like someone throwing a great party who slowly throws out everyone interesting because they want to be the center of attention. Once all the interesting people are gone though, the partiers are trickling out, and the interesting people who made the party hot have moved on.