Bernard being a part of the cult of Dionysus and being sacrificed and it wasn't a success but it also wasn't quite a failure and the power stays dormant there. A few years -or months- later he dies and that bit awakens which will revive him with the powers and a bit of the amorality of a Greek god. Tim eventually also dies like future state (maybe exactly the same way, maybe while saving Ariana coz I love Tim's first love), but because of his grief, anger, and growing apathy largely caused by Bernard's death, the Lazarus madness gets a stronger hold and he just doesn't try to shake it off.
All for the chance for it all to come together:
The Witch (Laura), the God (Bernard), and the Immortal (Tim).
And they call themselves The Grieve -well, they eventually decided on it even if Bernard was very insistent on Grieve Gang- not only because of the school that brought them together but also because each one died and came back and had been grieved by the others.
They go on adventures through space and time and magic just harassing the universe, you'd stumble on them having margaritas on Apokolips, or setting New Genesis on fire, and one time for exactly fifteen minutes they took over Oa. They also allegedly stole Zeus's thunderbolt and switched it with a fake that just farted every time the god tried to use it because of course Dionysus would. Allegedly.