Tuvalu is still a sovereign nation and as such can repudiate any and all contracts at will. Look at recent history and you see there have been several instances of countries "nationalizing" entire industries (oil/banks/etc) without so much as a dime to the former owners of infrastructure or equipment.
A change in govt there, a coup or somesuch could easily bring this about.
Now do I think such a thing is likely? No, but it is an issue to be aware of and one should keep a reasonable watch on news reports coming out of T.