What they ended up doing was Deus Ex Maquina or God in the machine. It’s a way to magically solve a problem without actually doing anything. In this case, they literally had the word of God tell them exactly how to do it.
The brothers open up the tablet that they stole for Roman and it contained the word of God written by Metatron. When they open it up, Castiel wakes up and the brothers head to the asylum to meet up with Meg.
It turns out Cas is a little off and isn’t really much use, but is willing to give up some of his blood for the good of the cause before disappearing. I guess his fight is over. A prophet is awakened to find and translate the word and Castiel’s old garrison is sent to grab him and take him to the desert. Yada yada conflict yada and he ends up giving the translation to the Winchesters.
The angels take the boy back to his home where there is a Leviathan waiting for them and it kills the angels. So, now the Winchesters have to collect the ingredients and kill Roman. Wow, how anticlimactic. As a writer, the use of Deus Ex Maquina is occasionally permitted, but for such a large plot point it seems like the writers just lacked imagination.