Well quite the fight going on, though the Klingon sure are gambling heavily with the attack on Andor. The only reason I can see for this is, is that their situation is becoming increasingly tenuous politically and perhaps also strategically.
Politically because things have stagnated but the war won't end, which is hurting their hold over the other Clans most likely. And the Federation isn't giving up because they can't give it a sufficiently large knock out blow, and so as all to often for nations in a defensive war, they doggedly try to hold on as they don't feel like they necessarily will lose. This tends to only be even more true for more Democratic ones that can be surprisingly stubborn about such matters. The end result is dwindling political power.
Strategically, while the Klingon apparently have some what shored up their supply system with escorts, this is not in this case probably a sustainable situation. As the Federation rather obviously will be building many more ships as fast as it can, and especially Excalibur class ships. The big problem with more Excalibur class ships is, is that if they can't manage a major attack... then obviously they'll just start grouping them together more with the extra ships and start convoy raiding in force. At which point it will likely become quite difficult even with D7 escorts to maintain supply lines. If the Excalibur didn't exist, this wouldn't be such a big threat, but Excalibur class ships have excessively long range and are highly capable of extended operations far beyond the normal logistical hubs. If I were the Klingon, I'd definitely think that the ship was designed specifically to ruin them in any long duration war... which perhaps it some what was.
Beyond these two factors, retreating from the war isn't really a choice as it would ruin the leading house Duras political legitimacy and hold on power. Meaning they must attack, but they lack time to setup the logistics for it before the Federation will be back with ever greater numbers of Excaliburs that will like to do nothing better then prevent that. As well as the risks of the war becoming attritional, which could leave the Klingons vulnerable against rival nations around them seeing potential weakness to exploit.
Thus they're gambling everything on a win or lose, get a core world and hopefully use that to spring board attacking the other core worlds. Or basically lose everything as they can not retreat. The Klingon ruling house basically probably disintegrates, the head probably dead and allies abandoning it. Thus leaving the Federation to now be able to pick off the now less organized house based Klingon forces in offensives. Most likely in such a case back to just the border as the Federation probably would not want to give cause for them to unify again by being too threatening. In this case the result would be a Federation victory and the Klingon probably not wanting to go back any time soon, it's not like they'll have less Excalibur and other similarly dangerous ships in future after all. Basically the Federation would probably get marked as more dangerous then they first looked and others will become more preferable targets.