Since he is dead he cannot be certain it will be achieved and in any case he will dead.
V'Latak fell into the trap of announcing his intentions as he injected himself in order to elicit an emotional response from Ambassador Sarek, one that would be seen by no one and had no logical function (a so-called "villain monologue"). This was a sign that even he, the most extreme logician in his mind, had blind spots and lapses in judgment. The logical way to achieve his goal (murdering Sarek to prevent a conference with the Klingons so that the Federation would lose badly in the War and Vulcan would somehow manage to secede peacefully... simple, I know), would've been to anesthetize or at least immobilize Sarek prior to exploding himself.
He didn't foresee Sarek having access to the internal forcefields, a major problem with V'Latak's plan. I understand he was under a time crunch, but like any good Vulcan, he should've been able to judge the statistical probability of his murder plan gaining success. I mean, he couldn't possibly realize Sarek's katra connection to Michael Burnham, who happens to be on Starfleet's only near-instantaneous warp ship, but other possibilities for survival persist (Sarek being quicker, Starfleet mounting a fast rescue mission, or even the Klingons or elders of Cancri IV arriving to assist).
The Logic Extremists make sense to me (although it would've been better to call them Vulcan Isolationists, thus referencing the TNG episode). 100 years prior, a Vulcan military administrator had gained control of the planet and used his position to attack Syrannites (followers of the true teachings of Surak), and plunge Vulcan into military conflict and espionage. Remember that Surak himself was painted as a pacifist (even if that doesn't always make logical sense). It took the Syrannites, guided by the katra of Surak, to overthrow V'Las and reform society. In the coming Babel Crisis, if not the Romulan War, the Vulcans withdrew many of their troops and did not participate at full capacity.
Flash forward 100 years, and you have a Federation, of which Vulcan is a nominal member (they have their own expeditionary force and way of doing things), which gets embroiled in an interstellar war with the Klingons over what seems to be an illogical misunderstanding. Thousands of Vulcans are dying defending this Federation led mostly by races that ignore the purity of logic. Surak was a pacifist, but his people have yet again found themselves embroiled in military conflict.
Enter a group of so-called "extremists", whose simple goal is to get the Vulcans out of the Federation by any means necessary. This isn't an IDIC issue - all races are free to live as they see fit - this is a life or death issue. As long as Ambassador Sarek lives, and is using his political connections to promote war with the Klingons, and even worse, the degradation of Surak's society (by literally and figuratively creating Vulcanized Humans and Humanized Vulcans, disregarding his procreational acts with at least one human female), then Vulcans will die in a war they had no part of making.
The needs of the many outweigh the needs of the few. V'Latak, and many like him, will willingly sacrifice themselves to remove these subversive elements preventing their homeworld from achieving pure logic on its own merit. Just like Surak 2000 years prior.
But, you know, it's probably just Romulans messing around, and I'm just overthinking it.