Even though Scott Pilgrim pays homage to everything I love in life from Zelda, arcades, music and even romantic fun times, I cannot get passed the fact that this movie wants me to root for a character played by Michael Cera who kills people. KO means knock out, NOT fatality.
I actually make mentioned of this on the IMDB.
Since the video game aspect is heavily played upon, it's safe to say that the Exes aren't really dead, and that they've just respawned somewhere else.
Ramona said that Scott had to "defeat" her seven evil exes, not kill them. And in the context of video games of the early 1990s, the bosses are never really killed, but just defeated and often end up coming back for a sequel. One such example is Mr. X from "Streets of Rage." Another is Dr. Robotnic from "Sonic The Hedgehog" he's been defeated multiple times and kept coming up as the main boss in the other Sonic games (he's even been defeated each level of the first Sonic game, only to keep coming back).
Now, we've seen all seven Exes burst into coins, but it doesn't mean they're dead, just defeated. I mean, Gideon even spoke to Scott after he was defeated through his glasses (before Nega-Scott turns up). And every time Scott has one taken out, they've been listed as "knocked out." Even in the comics, there's no evidence suggesting that they've been killed, just defeated. One person at the IMDb stated that they had to be killed, as Clash at the Demonhead broke up after Todd was defeated in the comic. But this was quickly shot down by others (including myself), because A. Todd got pwned by Scott, who was weaker than he was (and that was part of the reason why Envy left Scott) and B. he had been having an affair with the drummer, so naturally Envy would have broken up with him even after respawning.
"But how do we know for certain they respawned?" Simple: Scott did. He earned a 1-Up that lead to a second replay of "Level 7: Chaos Theatre." If Scott can respawn, its safe to say the Exes did too (even more evidence of this is the fact that Ramona says at the end, "The past keeps catching up with me", indicating that the Exes would more than likely show up again).
The point is, the film is a video game, so the Exes aren't dead, just pwned in several different ways by Scott Pilgrim.