Umm...no.
Laroth doesn't hate the Sidar. He likes them more than anyone, because although they think they serve Arawn they have long been serving him. The Sidar didn't steal his tomes, the Once-Elves did. The Sidar were never in his empire, unless you count Rathaus Denmora just barely entering it to talk to an angel in his service thinking he was going to serve Arawn. I doubt that the Sidar know Laroth exists. The Sidar got these books from the Malakim, as Varn (or, more likely imho, his wife Talia) Gossam took them out of the Shadowed Vale, after Varn's father had taken them from Laroth. He likes that the Sidar use these books, and very well may have meant them to be found. The rituals don't just slowly devour their souls to give long life, they slowly transfer their souls to Laroth for him to use to gain power. Laroth forged the Netherblade out of stolen souls specifically to give to Rathaus Denmora so he could capture more, stronger souls to help him defeat Arawn and become a god.
Duin and Charadon didn't just "come back," they were resurrected using powerful life magic that became available only after Sucellus was resurrected. This wasn't possible until recently. Hmm...on second thought, such power might have been available from within the netherworld when Arawn was god of both life and death. I'll just assume it is something that must be used in the plane where one is to be resurrected though.
I'm not sure he would want to be resurrected anyway. The netherworld is much more responsive to his will, and his Spirit magic is more important there. He probably wouldn't want to return until he ascends to godhood. (Hmm...would he even be bound by the Compact and thus vulnerable to the Godslayer like the other gods, as he wasn't around when the Compact was signed?)
I see no evidence that Decius is a sorcerer of any kind, much less one so strong as Laroth or Kyorlin.
