My party landed in the final witchgate at Renchurch and 3 of the 4 were instantly killed by the banshee standing guard. One of those 3 was the cleric wielding the Raven's Head mace. The fourth escaped, and plans on returning to Caliphas (or somewhere) and recruiting new help to return to Renchurch.
My question is, how do I get a new party in there? What should be different for their journey? And what should the Whispering Way do now that the Raven's Head was dropped at their feet?
I assume it was the 140HP of damage to each of the players from her wail? That's brutal. I'm not there yet in my campaign, so I can't really comment on what you should do now...
If the sole survivor remembered that it was a Teleport-type spell that landed them in the final witchgate, a Knowledge Arcana roll by a competent arcanist might discover the possiblity that multiple teleports would deposit them in that gate (I believe the book has DCs for those checks to understand how the Witching Gates function). So if you don't want your party to go on this unnecessary drag again to get back into the action, the witching gates can be "exploited" to port your way directly to Renchurch.
That late in the game just tell the players not to worry about RP aspects and just Herolab up some toons to finish. In fact you might want to encourage cheesiness with Glory/Sun clerics,Ragelancing barbarians, TWF-Fighters. Being able to wreck face on what killed them the last time is great therapy.