so you can only do a quest once in offline mode

[x2]

so does that mean whe someone says "i do a ton of forest of sorrow runs each day" that he quits the game whehn he/she gets the item he/she is looking for?

[GuerillaPimp]

Nope, once you finish all 25 quests, they all become replayable for that specific difficulty

[Blue-Hawk]

yes and no.
yes- he/she does.
no- he/she completed every quest thererfore reopening every quest for unlimited completion.