Just to clarify the Tuvalu flights were not a part of the award ticket.

Your best best is to call and make a change in the return ticket -- either of dates or to drop segments. Don't risk if the airlines communicate or not. If they do you have serious problem. Now you only have an resolvable issue (perhaps with a fee), if you get cancelled out it is much worse.

For communications get a phone card or Skype or GoogleTalk or ....