Can you play this card from your hand like a normal quest?

According to it's text, you begin the game with this card in your quest zone and with one random card from your deck on it.

So if you decide to take this card in your deck, you must put it in the game and cannot mulligan.

Quite odd.

If the card gets destroyed and ends up back in deck (then hand) you could play it.

If the card gets destroyed and ends up back in deck (then hand) you could play it.

Remove 3 resource tokens from this card and sacrifice it to take the card attached to it into your hand

Heroic task is sacrificed and goes to discard pile. But the attached facedown card can either go to your hand, or (if it's an artifact) can be attached.

I think, that if HT has been put out of play, you cannot get it back in hand.

Why? If it is in discard simple Order in Chaos brings it back.

okay. and now it's time we should summon Mallumo! =)