Eyring's position on the Q12 is for lifetime, but his position as counselor isn't necessarily the same. It's been customary for the past several several First Presidencies for counselors to be retained, but it's neither doctrine nor official tradition. If Nelson wants to keep Eyring as a counselor, he'll remain as acounselor. If not, he'll go back to the Q12. We'll all know soon enough.
I think he should go with Rasband and Renlund (or was it Raslund and Renband? meh.) Picking a younger fella from the back row (they're both 66) might evince some good p.r. that they're trying to push the slightly less elderly leaders to the forefront (though it wouldn't change their seniority status of course.)
Don't forget they also need to replace Hales on the Q12, probably at the April conference though I think it's highly unlikely a newly chosen Apostle would get selected as a counselor unless he was someone already well known to Nelson.
Dieter is a fan favorite - I can't see Nelson sending him back to the 12. TBM Bro-dudes also have a serious crush on DoDo, so I wouldn't be surprised if he replaces Eyring.