Games don’t kill other games. If Dirty Bomb dies, it will be killed by Nexon and Splash Damage (ignoring major issues such as hacking, making silly design decisions such as the melee changes, focusing 90% of their time on the cash shop instead of making the game better etc).
If this game was truly a masterpiece, people would still play it no matter the competition. Someone else mentioned earlier that they think DB could die before Overwatch is released, and that is certainly plausible. Not everyone will be invited into the closed beta testing later this year, and by the time it is fully released (just before Christmas knowing Blizzard) Dirty Bomb could well have died.
Certainly the last of the mercs should be released by then, meaning content updates will likely consist of bug fixes and balance changes which isn’t exactly going to keep people hanging around.
It has only been 2 months since open beta began, and I predicted Dirty Bomb would likely be dead after 6 months (by dead I mean further development will be dropped as the playerbase will be too small to support ongoing development), and given the past 2 months I stand by that.
Even though the game is fun, it is lacking in depth, the skill floor is too high for casuals (making many of them a burden on their team because they can barely aim) and the skill ceiling is too low for competitive players. It isn’t much fun to watch either, so eSport potential is very limited. There also aren’t enough maps, but given the above, I doubt it would make any difference if there were dozens.