If you trust canaries AT ALL, you trust that an LEA can't make the owner sign it under duress. Otherwise they don't work, since the owner could just be forced to sign it without missing any window.
Then, it stands to reason that if the canary gets updated again, you trust that everything is fine again, and that the owner didn't get served with an NSL. Therefore, it follows that if you trust canaries at all, you cannot stop trusting them if they fail to be updated for a time, except for that specific duration.
Please correct me if my reasoning is wrong anywhere.
The failure modes of canaries are safe because they die, the fragility is the whole point.
Once dead they tend to stay dead. If you then prop up the canary afterwards and say it wasn't really dead, we just forgot to feed it for three weeks you're risking credibility at a minimum.
So either the operator is incompetent (which makes them a bad choice for trusting them with critical data) or the canary is now potentially under control of another party.
The problem I have with the whole setup is less one of whether or not this is a 'fixable' issue and we should redefine warrant canaries and give them a re-incarnation option, it's that if you think the chances of getting slapped with a NSL or warrant are large enough to have a canary system to begin with that you're dealing with customers that are - or should be - paranoid enough that any tampering with the system other than behavior as explicitly stated up-front should be un-acceptable.
Otherwise it becomes a question of where do we draw the line? A few weeks, a month or a year, what point is there to feed the canary at all if you can revive it at some arbitrary point in the future. After all the canary is a channel with very specific conditions attached to it, it now seems as though you are trying to redefine those conditions after the fact and that is the one property a thing like a warrant canary does not have.
If silent circle would have stated up front we will feed the canary weekly + a potential month in which we will take a holiday and everything is fine, otherwise we have been served with a warrant then you could call this operating within allowed parameters.
But I don't think you should be able to tack on such a clause afterwards.
Then, it stands to reason that if the canary gets updated again, you trust that everything is fine again, and that the owner didn't get served with an NSL. Therefore, it follows that if you trust canaries at all, you cannot stop trusting them if they fail to be updated for a time, except for that specific duration.
Please correct me if my reasoning is wrong anywhere.