If the Main dies, the leaderless team would also die.
I definitely disagree with this statement. There are many occaisons when the Main dies accidently in battle, but the opposing forces are almost wiped oout, with the entire team alive- had the player been allowed to continue the battle, the player would've definitely won. This arises mostly from carelessness, or long difficult battles. Here are two contrasting examples: the Main gets killed during mission one against the Mech Captain, with only the latter remaining and all teammates alive and in full health- the Mech Captain doesn't stand a chance; the Main gets accidently killed from one of the three Spriggats assassins, when there is only one Spriggat remaining with 4 health and 3 teammates surviving. In both cases, the team can take the corpse and quickly leave the place. In the latter case, there are no other hostile forces in the area (the patrols have already been cleared and only 3 assassins were waiting for them), so it shouldn't be a problem for the team to back track (there is a clear path leading them out of the Great Forest).
Also, and these are killer examples, I think: the Main can die battling Giant Bugs in Somnus (ok, they can eat the body, but!), the Main can get killed by the Vargant or by Flavian. In two latter cases, this happens right under Tastidian's nose (he'll know, through the Slave Bracelet, if the slave is killed, and quickly hop on to find out why, and that's a very short trip to both Flavian's and to the Vargant's), the Main is killed with Mind Blasts, which would definitely leave the body intact. Flavian, being x-military, would not dare eat the dead Main, as he's the property of one of the most senior (if not the most senior) Shadowlings in Shadowling military, and he's just outside on the street- Flavin is no use to Tastidian, but the Main is. Also, Tastidian will react quickly to the Main getting killed and be there in no time at all, to prevent any feasting on the corpse (this applies equally well to the Vagrant case). Hence, the corpse is not the point in case of Nelis (but not Luca).
If the Main sides with Tastidian, it says that "eventually" the war is won, but that does take time, so in the long run, the tide of war goes against Spriggats, but in the short run, they might've managed to put up enough resistance for Shadowlings to get the message across to them.
I agree, Noctus and Shadowling Loyalists seem to be very well suited for each other.