I'm not sure I understand the lore well enough to really say. Gale explained that he wanted to return it to her, and that absorbing it was never his intent. From what he explained about how the shadow weave worked and what it was, that intent seems to check out. My understanding of it is that the fragment of shadow weave was basically normal weave 'stolen' from her and corrupted/altered, so Gale's intent was to return it to Mystra so she could change it back. I didn't think that the shadow weave itself was harmful to her so much as the way it was created and used harmed her. But my understanding is hardly complete, like I said.
i think absorbing the shard is gale's intent.
because i used to have the dialog with gale -- "Mortals should not attempt of becoming a god." gale replies -- "we sholdn't worship a god blindly, we try a way to be close them , isn't a wrong thing."
this proves that absorbing the shard is gale's intent.
i tell gale, we shouldn't pursue the power that we can not master. but gale's answer is that -- "why not? if i have the chance i would like to be a god-like being."
if you say gale want to return it to her. i think gale means that i have bound with the shard, and mystra should favor me again. but mystra's choice is that -- give up gale. i suppose the issue could be that "who gives the shard to gale".
