[MAGNAT2645]

The thing is that you can't block event execution with HookEvent:
1) You're using EventHookMode_Post which executes after event.
2) Even with EventHookMode_Pre you can't block event from execution. If you return Plugin_Handled (using _Pre mode) you just can block event broadcasting (for example, "player_death" shows top-right label "{NAME1} killed {NAME2}", so you can just block event broadcasting for clients but the event itself will still happen on server-side)

If you really want to somehow block Source-engine events, you need to write your own C++ extension, i think.