Ok so, I need to reball this thing and my supplies are coming later today.
Before I reflow it I should probably try to desiccate it a bit more though.
IPC guidelines seem to suggest I should bake for 9 hours at 125C but that's probably not practical given that my oven only runs for a max of an hour at a time and so I'd need to be around to reset every hour. But I'll do as many 1-hour cycles as I have time for before I reball tonight.