Death trooper is the only character than can inflict death mark on demand in the way needed for this team to work. Darth revan is the only other character that inflicts it at all unfortunately. That makes DT basically essential.
If you are looking for a replacement for Pao you'll want someone that can give the whole team offense up, but is preferably also an attacker, hence the suggested replacement with Anakin. The team works okay with a gear 8 Pao though if short of stung guns (who isn't). Emperor palp is another option but you lose the benefit of having 5 attackers.
If you are looking for a replacement for Chirrut, Rex is the usual choice. Provides the same function of giving tenacity up / cleanse as Chirrut but again, isn't an attacker so you lose that benefit. (There's also some issues with turn meter management when using Rex but it still works). Chewi is the best replacement though, does most of the useful stuff needed from Chirrut and also has a higher offense stat.
I'm anticipating the flame I'll get for saying this.... but I actually ran Chex with snow trooper for a while after it was first theory crafted (he was the highest offense attacker I had at the time and I didn't have Chirrut geared) and yes, it requires a few more restarts than when you have the cleanse from chirrut, but you could still get high damage runs... it just took a longer time with extra restarts. (I don't recommend this... we needed all the help we could get in P3 back then).