Does the spell cast with Yahenni's Expertise resolve before state-based effects are checked?
Your 2/2 will be returned by Living End. 

The "cast a 3cmc or less card for free" is part of the resolution of Expertise, not a trigger like other cards/abilities (like Cascade).  Even though you cast it as part of the resolution, the free card does not immediately resolve, instead it is put on the stack. At that point SBA are checked and then it can be responded to.