Earlier quoted context omitted.
Tuvalu is a country. It became an independent nation in 1978 and is a member of the UN.
YEah it will be interesting to see how it can be treated if it has no territory . Technically most of UN conventions require territory to be applicable. Territorial waters are defined based on this land, which has to be natural. Most likely this will be treated like when a country invades and destroys another: .TV will cease to exist and its citizens will be absorbed in other States.
Why should they ever get to a position where they have no land? Even the worst sea-level rise predictions states that the sea level will rise only by around 3 metres in the next 100 years or so and about 10m by 2300.
3m is just around 9ft. And we are talking about less than 12000 people living in about 25sq.km of land. It would be trivial to increase the height of the land by a couple of metres.