This dialogue doesn't really establish the degree of "hurry", beyond it being "less than ten years". Supposedly, the collector, if working as promised, would solve the problems very quickly, so applying collected salvation at the nine years, eleven months mark would still work. So if the Council asked for assurances, refusal to provide any would still appear suspicious. "We will have a demonstration ready in two months" should be followed by "Okay, we will give you the mandate in two months then"; "We will have a demonstration ready in two years" should be followed by "So you don't have any idea of whether this is going to actually work? Please come back in a few decades", along with sighs of relief that Rua'fo wouldn't be among those returning.
This wouldn't work too well if we assume the Son'a are a subset of the Ba'ku. After all, the Son'a supposedly can't breed, yet were "rebellious youngsters" when they left and supposedly very soon thereafter began their own disastrous experiments at longevity so that many of them still survive after those centuries. How much breeding could have taken place before the experiments? And if the Son'a were a majority originally, why did they have to leave while the minority of 600 stayed?
If we instead assume the Son'a are the originating culture from which the Ba'ku originally fled, and the "rebellious youngsters" just returned home where everybody subsequently engaged in the longevity experiments and thus lost fertility, we could indeed say that some 600 were facing the horrible fate of not living forever while millions or billions of Son'a could simply go live on the planet for a while and thus become fertile again and possibly also immortal. But giving the Son'a a home base of billions of loyal natives (never mind the slaves who could be more a threat than an asset) plus the evident tech advantage would make it less plausible that they'd need the UFP for anything at all.
Timo Saloniemi