The only problem with answering how things would've been different
is that some information might get out by inference about how things might
still *be*. However, to do what I can with the question (never let it be
said I don't try to accommodate....).

If Lyta had stayed on B5, her arc would be pretty close to that of
Talia, except that she would have begun to form a strong link to Kosh,
first in the form of dreams, then something with implications that could
be read as menacing or benign.

If Dr. Kyle would have stayed around, he would have moved more into
the position of advisor/paternal figure for Sinclair. He also would have
continued to be more scientist than doctor.

Takashima would have been revealed as having been in on the Vorlon
assassination attempt by season's end, and would have betrayed Garibaldi
in the events in "Chrysalis," either giving him over to those involved
with the coup, or pulling the trigger herself. While we would know this,
our characters would not, for as much as another full season.

Carolyn Sykes would've gotten into major trouble with one of the
major EarthCorps.

Finally, if Sinclair had stayed with B5 at this juncture, the events
in "Points" (the reveal of the Minbari surrender) would've taken place in
episode 3 instead of 1. Episode 1 would've consisted mainly of the events
in "Revelations," which was mainly as a bystander to the events around
him, since the sister aspect specific to Sheridan obviously wouldn't be
there. Basically, with all the events surrounding Delenn, Londo, G'Kar
and others, he didn't have one whole hell of a lot to *DO* in the first
six to eight episodes, since that segment was set aside primarily to
introduce the Shadowman war and get that cranking, and Sinclair had no real
direct connection to that.

jms