See article http://time.com/4691046/puerto-rico-american-citizens/
Are Puerto Rican's full US citizens?
Can US unilaterally strip their citizenship?
Some of the above and many other questions appear to be central to how the US deals with Puerto Rico, the debt, and the political status of the island. There are differences in the percentages of Federal aid and the removal of SSI for example that seem to be tied to the status and how the US goverment sees Puerto Rico. In a way it is a US territory and in another way it is a foreign country.
If PR becomes independent in the future, will the Puerto Rican's be stripped of their citizenship? Will the US Citizens living in the island be required to get Puerto Rican citizenship? Will they need Visas, will they be able to have properties and land?
Obviously all of that and many other questions would be resolved if PR becomes a state, but it is far from a done deal. I do not expect PR to settle on its status with congress for at least another 10 years.
Lots to think about.