If he's essential, he still gets into a fight with the guard, which I want to prevent.
I haven't decided where Lathenil should "go into hiding" as he writes in
Rising Threat III "
I went into hiding, waiting anxiously for word of the Thalmor's activities back on Summerset Isle." One possibility is Gweden Farm! Especially if I have Silanu help him work on his anger management.
His narrative indicates that he survived longer than Ocato, and only got to meet him just before he was assassinated in 4E10 if his "decade of machinations" is an accurate figure. That should make him a useful character for other quests, if I can think of them.