You have 3 basic options that I see.
The party gets magically reformed somehow and the old PCs carry on the fight.
I only know the basic concept of the campaign, but you never have to run things by the book. Not everyone is going to want to do this, but you could have the PCs brought back. Either it was a dream/simulation, a warning sent by someone that they could easily fail and die. Or there could be some other being that gives them a one-time-only get out of jail (death) card. Perhaps the group wakes up to find themselves dead and trapped in some kind of prison that they need to escape. Of course there's always the old "the BBEG captured them and really just knocked them unconscious" bit.
There are a lot of ways of doing this, but it's not going to be for everyone.
A new party picks up basically where the old one started off.
This has already been alluded to, and is probably what I would do. As far as knowing things, one of the party could simply be a relative of one of the dead party members, come to search for him. The party member, unbeknownst to the others was sending back messages (possibly using magical sending stones). This accounts for some knowledge that the players will know that the PCs will not.
Alternatively you can just have spirits pass on information in dreams, etc. Even if the mod forbids it, you're the DM and if you can come up with a reason, then it happens.
You start a new campaign arc.
Honestly, this is generally what I've done when I had TPKs. The world goes on, the bad guy wins or partially succeeds if it's an end of the world kind of thing. Then again I don't use published campaigns very often or heavily modify them for my own use so you may want to get more use out of the book.
Combination
The BBEG has won, or is winning because the heroes failed. You play a session or two with a different party and the aftermath and potentially a pretty desolate world. Some divine being/god decides they don't want this and send a party back in time to pick up where the old group failed. Show the players the consequences of their failure before they get a chance to fix it.
Good luck!