I can't think of any actor who, upon not getting the series gig, would
be willing to come in for one episode at the top of the show to say goodbye,
unless s/he had been on the show for X number of seasons. Also to follow that
model means we have to deal with 3 characters going, and 3 characters coming,
for 6 exchanges, in a one-hour episode, which leaves little time for a decent
plot. It's simply not workable.

We will, though, be phasing in the changes over time; Ivanova in the
first episode, Dr. Franklin in the second, Catherine well down the road.
This spreads out both the exposition and the impact, and lets us focus on the
stories, where our attention really needs to be placed. There was an awful
lot of exposition in the pilot, and I'd rather not fall down that particular
rabbit-hole again for a while....

jms