Donatello rhetorically asked them if they had the power of God (which was required to seal the Darkness the first time). They don't, but there are objects that do, introduced in season 11 - the Hands of God.
I think the writers are going to end this season (and the series) with a heavy dose of nostalgia by going back to fan favorites. They already brought back Kevin, Amara, Eileen, Donatello, Michael/Adam, and the Demon tablet. They already alluded to Jody and Donna, and Rowena is now Queen of Hell. My guess is, we're gonna visit a ton of old stuff before God is sealed away (maybe with Amara's help), including the Hands.
Here's hoping for the Alpha Vampire and (the old) Death. Like most fans, I wasn't too sure about Lisa Berry as the new Death, but she definitely proved me wrong. She pulls off the "detached to stay impartial, yet slightly annoyed that I now realize the people whom I despised (and killed me) are actually very important to the world" vibe. However, I'd still like to see Julian Richings as Death one last time, before the shows ends.
Would love to see Amara standing up to God in favor of Creation as well, but I get the feeling that one episode is all we're getting of Emily Swallow.