It says you should look around for caves and tombs around the Thirr. This is nice as long as we have only this realese but as soon as we have more this becomes problematic as the area will grow gigantic and it may be better to specify its location more, otherwise one may search forever.
After having given the poor ex-deadra possesed guy the proof or your killing of the witch(didnt kill her she gave me her broom) the quest ends even though the original questgiver should be the one who ends it and says that you completed it otherwise it looks weird if she just gives you a new mission as if nothing happened.
EDIT: Based on the discussion on Discord there is a solution of letting her say something like "Thanks for curing Theodus, now..." when asking her about orders.
If you agree to help the Witch find out who put the bounty on her head and then kill the deadra of the poor guy in the Fighters Guild you are stuck because he only tells you as much as that the scout came with the order but you can neither ask the scout about it nor can you ask the poor ex-deadra possesed guy about it again. So your stuck if you want to go down that quest route.