iirc you can't continue a classic game in DE, but about that act 3, if you mean namelss isle... I suggest a respec so your entire team does magic damage, or so your entire team does physical damage (at least 1 necro and 1 ranger). And at that point in the game it get's a lot easier if you have teleport/nether swap on everyone, and focus on landing good shotgun abilities at the start of the fight; there's only one or two fights in act 3 that you can't oneshot the entire enemy team with some good shotgun hits (blood storm, thunderstorm, mass corpse explosion, pyroclastic eruption, etc). It also gets a lot easier if you have chameleon cloak on everyone and build pure damage.