I just stop the questline as soon as I get Shadowmere. :hehe:
I use this concept alot. I think there are far better places to 'rest' most questlines than at their completion. For the MG and FG, I find this is before losing too many guild mates and innocent people (eg: Burma MG guild, Waters Edge for FG).
I believe there are several such choosing points along the Main Quest.
Although I have zero sympathy for LL or his heartless cronies, if doing the DB questline, it certainly makes more sense to stop progressing before the purification (unless of course you are just trying to infiltrate and destoy a nest of psychopaths anyway).
I find it is really only the TG that reaches a satisfying conclusion - it is a love story, after all. ^_^