Most of the characters that Greg has killed have been minor...
Let me make a list of dead people:
2) The Makuta in general
And that's it. Those are the only characters we met that actually dropped dead. Greg has a really bad habit of bringing back dead people, and the Red Star snafu just proves it.
There are three ways to die that will ensure that you stay dead:
b) Absorption (by a Makuta's shadow hand.)
c) Digestion (if you're eaten, you'll break down into nothing and threre won't be any body left.
Basically, if you lose you're body, no revival for you. Let's remember that the Makuta of Stelt and Spiriah were killed by absorption and were confirmed by Greg to be dead permanently, so anyone else who died like that is permanently dead as well. With that in mind, let's fix this list:
2) The Makuta in general (which equals around 13 named characters and 100 in general)
3) Ancient (disintegrated)
4) Carapar (disintegration)
5) Karzahni- Being (body hasn't vanished yet)
6) Tren Krom (confirmed dead permanently by Greg due to being organic)
7) Decoy Tuyet (body never disappeared)
8) Reysa (eaten by Rahi)
9) Gadunka (eaten by Rahi)
12) Morbuzakh (disintegrated and also is a plant)
12) Karzahni- Plant
Possibly still dead: Kodan, Nikila, and Naho (we don't know how they died so we can't be sure)
Add the multiple permanent deaths from Alternate Dimensions and you still have a pretty long death list, even with the Red Star, which, if you think about it, only really revived around 5 named characters as far as we know. Also, It's clear from clues and what Greg has said so far that the condition of the revived beings on the star is most definitely not sane or ok, so it's no party.
Anyways, I don't think it's past Greg to kill a Toa Nuva, but there better be a reason for it. As for who'd I like to die, no one in particular. Maybe an OoNM member.
Let's keep in mind that we are talking about major characters here, so rearranging the list:
And even in this list some characters aren't really that major, like Certavus and Carapar.