Disclaimer: I am not Mercedes Lackey, and I therefore do not own Urtho, Vikteren, Shaiknam, Skandranon, Ma'ar or any other persons or places you recognise from her novels. I am making no money off this, so kindly don't sue me.
A/N these are alternate possibilities to the end of the Black Gryphon. I've always thought there were so many other things that could have happened.
When Aubri crashlands with his tail afire, he lands on top of Shaiknam, instead of next to him, breaking Shaiknam's neck. The whole betrayal episode simply does not happen. The tower is still evacuated, although rather later than it would otherwise have been. Only one explosion occurs, and it is smaller than it would have been due to the fact that some of the potentially explosive objects have been removed or taken apart. Urtho and his forces lead a guerilla war from in hiding.
Aubri does not attempt to enter Shaiknam's tent when he overhears the traitorous conversation. Instead, he flies over to 5th Army, and warns them about Shaiknam's betrayal. He then uses a gate set up for him to get back to Urtho's tower. The pass is not overrun for a week and a half. Conn Levas is arrested as soon as he arrives at Urtho's tower. The tower is evacuated with much more time to spare, and the bang is much less explosive, and the second weapon is brought with them unused. Urtho survives and leads a guerilla war.
One of Urtho's generals manages to convince him to go on the offensive early in the war. Urtho's army wins, Ma'ar is killed, and there is no cataclysm. Ma'ar may turn up in another body 100 years later... unless he is killed before he invents his little hidey-hole.
When talking to Skandranon and Vikteren as he is dying, Urtho decides not to tell Skandranon about the weapon, with the result that it is not used. Ma'ar survives, but is so busy cleaning up the mess caused by single explosion that he does not follow the refugees. Several groups of refugees start conducting a guerilla war. They get really good at it, and Ma'ar's army gets bogged down, and starts having major attrition problems. There is grumbling in his own lands, both because of the mage storms and because of the guerillas. He ignores it, or reacts harshly, but which he does at any given time is rather unpredictable. His own people are starting to turn against him, while the conquored people are being as unpleasant as they can get away with. Urtho's army reorganizes itself and starts working with the conquored peoples.
Urtho does not tell Skandranon about the weapon, and it is not used. However, Urtho lures Ma'ar into his tower, and both of them die there. Ma'ar's empire falls into several warring states in his absence, partly because of the mage storms.