"Near" impossible ? Does it mean it happened before ? How'd it go ? Like an amputation that left permanent emotional damage ?

Does that mean Matilda can't use her wish to go home?

Matilda is part of a different type of setting from the 'Toon Core' aspect.

For the likes of her, Rose Hips, Fujimi, and some others, they've experienced a situation of being 'Toonekai'd' by the entity known as 'The Cartoonist'. This means that they've been pulled out of their own reality and placed into an alternate toon world with their new selves crafted around the world they have been put in.

It would still be possible for someone Toonekai'd to find their way back in some manner. Matilda making that kind of wish likely wouldn't work.