SPOILERS: Gale has in his posession the most powerful healing spell in the world of D&D outside of maybe "wish". True resurrection can bring a 150 year old zombie back to life at full health. This spell cures ANYTHING, mindflayer tadpoles included. It is a 9th level spell so powerful if the only thing left of you was your big toe your entire body would grow back from it, it would pluck your soul from the netherrealm and shove you back in. You would be like a new born baby.
The number of clerics or druids that can cast this spell would be probably countable on one hand in the entire fogotten realms, it is also INSANELY expensive to cast. The only divine magic more powerful than this spell would be that of the higher gods. As such if you cast cast true resurrection on gale and he still has the bloody tadpole the chances of finding someone to heal you outside of a god is naught. Not happening, end of story.
When you first meet gale he asks you are you an arch/druid/mage/cleric? You answer no obviously. Gale being an academic know it all, he would know full well his "true resurrection" spell is the most powerful healing spell any healer in the world would be able to cast. He also clearly understands its usage. Mmmm. This is a quite painful story plot hole. This paradox shatters the entire story for me.
Gale has a magic void in his chest that feeds on powerful magic. The tadpole is enchanted by powerful magic.......See where I am going here? The void is also the same netherese magic used in the tadpole. I know if you suck the magic from a tadpole you would turn into a mindflayer according to that geezer in the underdark. However you could still use gale to suck the magic from the true souls tadpole and have the resulting mindflayer/s go nuts in the goblin camp.
That said if you could dispel the magic from the tadpole with gales glory hole you would have half the solution yes? All you would need to do then is get someone to remove a normal tadpole say the hag and drum roll.....meh.
I agree with the premise that the strong imposing nature of your companions like lea'zel, who basically thinks of you as dog dirt under her boot, very unlikely to remain in your party unless of course she enslaved you all. If you were gith of a different creche and cast she would still be overly critical unless of course you agreed with her zealous devotion to the lich queen. She is like an anti-paladin. Gith are xenophobic to an extreme level. The Kith'rak said it in a nutshell, "question, kill, move on".
