I don't think you can be a cleric after your goddess dumps you?
Mystra however just dumped him from his status of Chosen, did she not?
I'm more interested in knowing how a level 1 character was boinking a goddess and playing around with Netherese magic items on the Astral plane.
I assume he wasn't meant to be level 1 to start with, considering he said it was his exceptional prodigious skill with magic that made Mystra attracted to him, though that doesn't actually make him being a level 1 character much less silly. Like even if we assume the tadpole is intentionally cutting him off from magic, why would it leave him able to access any? Why let him gain strength again? It's a pretty bad background that requires a lot of handwaving to make any sense.
Also creates plot issues with making a satisfying power progression and lead up towards the ending. Like how do you end up feeling like you've really become a great hero or master wizard when your characters backstory is being budget Elminster, beloved of the goddess of magic herself?