WR already have rules around what constitutes an interruption of residency, and what not. IMO they should/could apply similar rules to those in this situation.
Yes, an exemption due to injury would be reasonable, as mentioned.
As for his specific case and going to Tonga to be with family, or whatever, he should be allowed to do so, without the new / delayed eligibility rules applying. He's broken, he can't play, but he was eligible at the time of breaking. Whether he wants to is up to him.
The tax laws use "domicile" rather than "residency". There is a difference and can be used in law. WR might be better to use it as well.
Surely we should be able to put in writing that we would have selected him if fit, at the very least have him travel with the squad this year to learn, even if he can't play.
That would be us putting our money where our mouth is and stop silliness getting around the rules.