How about this?:
Martok dies, leaving the Empire in disarray. Once again a civil war threatens to break out, but Worf retrieves the Sword of Kahless* and claims not just the Chancellorship, but with the support of Kahless's clone, the throne itself. Emperor Worf's rule is just settling into feeling like an established fact in the Empire when the Romulan home system is destroyed.
There has been long dissatisfaction in the Klingon general population with the fact that there are worlds that once belonged to their Empire that have been occupied and disputed by Romulans since the previous Klingon civil war. The Federation has been mediating these disputes and attempting to keep the peace, but now, with the destruction of the Romulan home system, popular opinion in the Empire is that now is the time to strike and take back what belongs to them by force - and Emperor Worf, feeling responsible even for those citizens of the Empire that live on the occupied worlds, cannot disagree. They attack, and war begins, since after so long, the Romulans see those worlds as theirs - feeling the need to cling to them even stronger now that their homeworlds are gone.
The relationship between Worf and the Federation becomes a strained one, trying to maintain friendship between the Empire and the Federation while making it clear that no interference will be tolerated. Ambassador Picard is assigned as Ambassador to the Klingons, and Worf's respect for his former commander sometimes only makes things more difficult.
After long years of war and a growing irritation with the Federation in the general Klingon population - because the Federation won't stop trying to interfere, both by launching PR campaigns within the Empire to try to end the war, and also by "providing aid and comfort" to distressed Romulan ships and to Romulan worlds left in ruins by the war, Worf is met, defeated in honorable combat, and apparently slain by someone who then takes the throne by right of being heir, ejects the Federation, and turns the Empire's sights on them, too - with the help of new allies that he brings to aid the Empire (displaced Jem'Hadar, maybe?). Emperor Alexander intends to unite both of the civilizations in his heritage - Federation and Klingon Empire -under a single flag and his own rule.