Yes you are!
The exact end of a quest depends a bit on the wording in the rules. Something along the lines of 'as soon as...' ends the quest immediately if the condition is met. There are other conditions that for example say 'if thisandthat is the case at the end of whoever's turn' which would give the heroes a little more time for looting.
IT IS ESSENTIAL that heroes have to set priorities whether to go for the objectives or take the time to get all the treasure.
If it is a relief for them you can tell them, that they will most likely get enough treasure over the course of a campaign.
How much treasure that really is, is up to them (as I already said). The scout treasure hunter/thief classes are especially nice for groups who like a bit more loot from the average quest.