When were the Tsen'kethi and Talarians mentioned? They've been tossed around before but I can't remember the episodes they were referenced in. (I'm betting they were DS9 episodes I never saw.)
Anyway, I would personally suspect that the Klingons would continue to be antagonist towards the Federation. Without the collapse of their economy and the brutal damage to their homeworld, they may be able to support expansion into any possible unclaimed territory they border. (or at least, undeveloped territory which they would've surely already claimed in the name of the Klingon Empire anyway)
This could put them on a better footing than they would otherwise enjoy, but without the Khitomer accords the Federation would have no reason to cool off on military development either.
Assuming that up until Narendra III the Federation didn't quite demilitarize (since Yesterday's Enterprise makes clear that the Khitomer Accords were not quite doing the job until after the Enterprise-C sacrificed itself to stop the Romulan attack on Narendra),
How so? The Ent-C may carry something of a military air about itself still, but that doesn't mean the Federation didn't put the brakes on starship construction. Shit, look at how we see so very few Ambassadors in service in TNG, yet we see
Excelsior class starships still operating out near the frontier and even old
Constellation class starships!
Granted, there are
a lot of
Excelsiors around, but even that suggests that Starfleet R&D was largely sitting on it's ass for some time, content to just keep churning out
Excelsiors and upgrades for them rather than build new starships.
I'm inclined to think that the Khitomer Accords in fact contributed to the Federation's seemingly imminent downfall in Yesterday's Enterprise, as it's possible the Federation was caught with it's pants down with a badly understrength fleet by the Klingons, and they never recovered from the Klingons' first strike.
I'm also inclined to believe that the Federation would still be slow in declaring open war against the Cardassians, although once they did that Starfleet would put significant resources into winning the war quickly and decisively in order to get it out of the way to be able to deal with bigger problems. However, if the Khitomer accords led to an anemic Starfleet in the 24th century, it's possible that Starfleet
didn't have the ships to do so in the actual TNG timeline without compromising Federation interests elsewhere.
UFP/Klingon relations are, in my opinion, a matter of political culture within the Empire. Gorkon and his ilk appeared to be a new breed of Klingon; one who saw peace as an acceptable alternative to conquest while still being able to maintain a martial tradition. Clearly there have always been those who disagreed with such a position; Kerla believed that such a transformation would "annihilate" Klingon culture, and the "religious fanatics" of TNG Heart of Glory also shared a similar belief. It has also been said repeatedly throughout TNG+ by various Klingons that the Federation alliance was somehow responsible for weakening the Klingon people, and in DS9 the Klingons readily invaded Cardassia largely for the fun of having someone to invade. (Changeling collusion? Just a convenient excuse, in my eyes; they wanted a fight and they found one.)
Praxis
may or may not have been the only way for liberals such as Gorkon to be heard and respected; without Praxis there may very well be a UFP/Klingon war, however if the Klingons should be ruined by such a war it could very well be a far more effective teacher than Praxis ever could be. Ironically, by finally having it out with the Federation and getting their noses bloody, they may very well come to respect and honor the Federation even more than in the canon timeline, possibly forging an even stronger alliance against their mutual enemy the Romulans.
While it's possible that such a war could be costly enough for the Federation to spark widespread pacifism in it's aftermath (a la the pacifism following the devastation of World War 1), it's also very likely that such a war would spur advances in military technology, as well as battle-harden a whole new generation of Starfleet officers. Generations of Starfleet officers who have never had to fight a real battle must have had a detrimental effect on the canon 24th century Starfleet Command, and without that detriment we could see a continuing military tradition within the fleet.
If this is the case, it's likely that following starships will be designed accordingly; and while Starfleet will likely continue the saucer/stardrive/nacelles configuration and eventually produce the Galaxy class, it's likely that this alternate Galaxy class would be designed in accordance with it's proper role as battleship; bringing to the field an awesome degree of firepower and endurance, it would be more than a match for the Romulan D'Deridex Warbird.
The fancy preaching about bettering mankind and finding peaceful solutions to everything is TNG-era
Heh, I don't think Picard had a peaceful solution in mind when he went charging into the Neutral Zone in "The Defector".