Based on something @rocketscientist said here, that replacing characters every so often makes shows last longer:
www.trekbbs.com
Imagine that at the time a Trek show was being made, you could make a character leave for whatever in universe reason you wanted, and replace them with a different character, all your own invention. What species and what sort of character? Who would they replace?
What would have changed in Seaon 4 episodes if Kes would still be aboard Voyager?
I have been thinking about what would happen if Kes was still aboard Voyager during Season 4. Assuming she still transported Voyager across this distance but managed to stay aboard (and the transport was a one - time thing that she cannot replicate). How would that affect plots of Season 4...

Imagine that at the time a Trek show was being made, you could make a character leave for whatever in universe reason you wanted, and replace them with a different character, all your own invention. What species and what sort of character? Who would they replace?