I think I'd have it be a River-centric episode, where she sees the end of his life (much like he saw her die in The Library). Make it the last River episode ever. I know she's probably traveled around with future Doctor's but to me her story will be forever tied to the Eleventh Doctor, so even though she knows other Doctors, we
don't necessarily need to see it.
I'd even mix things up and make it a quieter, more character-driven story. Lay off the sonic screwdriver and the running and the big monsters. Make it more personal.