Star is right in his assessment that another war with the Dominion is inevitable - the Founders are just too paranoid and xenophobic to allow anybody else to remain outside of their control.
However, another Dominion War is problematic given that the Dominion pretty much as the logistical and strategic advantage over the Federation and co., so there's no way Starfleet can possibly win in the long run if they engaged in a straight fight against the Dominion. Thankfully, there's still the Bajoran Wormhole being the key chokepoint the Dominion cannot avoid whatsoever; if they want to get at the Feds, they have to go through the Prophets first... and the Prophets don't really like them that much (thank you, Emissary Sisko!). So therefore, any war that occurs has to be more one of words and proxies... mostly likely, at least. Hiver could have other plans to deal with that issue.
Now, as for how to deal with the Dominion:
1) First option would be to continue dialogue with the Founders and somehow slowly curb their extremist tendencies and become more egalitarian. Very difficult to achieve, and not likely to succeed, but possibly the best option available to avoid any bloodshed on all sides. The best choice for achieving this would be Star and the other AIs, but... this comes with the obvious handicap we've just witnessed: the Founders creep the fuck out of Star, and the other AIs probably aren't going to like the Founders very much either. Their hesitance or refusal to deal with the Founders face-to-face would be the primary obstacle for achieving peaceful relations with the Dominion.
2) Second option in case the first one fails: sic the Borg on them. As crazy and suicidal as this sounds, there is a method behind this madness: we have no recorded encounters ever between the Borg Collective and the Dominion, and given both sides' respective philosophies, military strength, economic productivity, and innate species advantages, both factions would be an equal match for one another... and would grind each other down in a bloodbath unseen in all of history. But! It won't be a bloodbath that occurs in Alpha or Beta Quadrant territory: they'll bleed each other dry on the Gamma/Delta side of the galaxy, and leave the rest of us in peace while they kill each other.
Now, there is indeed a great amount of risk involved in this plan, given that Borg assimilation and transwarp capability gives them enormous advantages compared to the Dominion, and the Dominion would not be happy at being manipulated in such a manner, so the Feds would still have to involve themselves to an extent to play off both sides against each other and prevent one from having too much of an advantage over the other; if managed effectively, Starfleet can hinder the Borg's logistical strength enough for the Dominion to fight on equal footing, while still keeping the Dominion pointed at the Borg rather than the AQ via diplomacy and intelligence.
In any case, we just have to wait and see what Hiver does.