1. Updated isWorldGuardAvailable() method to check if WorldGuard is installed and enabled on the server.
2. Updated isPlayerInRegion() method to only use WorldGuard if it is available, avoiding NoClassDefFoundError when WorldGuard is not installed.
3. Corrected the onPlayerDeath event handler to properly decrement the remaining lives of a player and handle the KeepInventory functionality based on the player's remaining lives.

These changes ensure that the plugin works as expected, even if WorldGuard is not installed on the server.