If Nivi won't post, even with a multitude of people trying to get them to, then clearly they no longer care about this RP, and therefore, their character. Or they no longer have time, but it would have to be a truely dire case if they have not even the ability to inform us of how bad the situation is, either way Nivi is gone from us for some amount of time it would seem.

We either need to find a new player to commandeer the character, get someone to puppet it until Nivi returns(if ever), or find a logical way for the Admiral to die, thus removing the problem of puppeting though creating major ramifications for the plot(Which might actually be interesting...).

No matter the situation though, I trust our glorious GM to see is through this.