Interesting idea. Thankfully you don't have to use a hex editor to do this as it can be achieved through scripting. There are two scripts that activate after wiping out: your mother's script at 0x1A8DD8 and the Pokemon Centre script at 0x1A8D97. Since the party Pokemon locations are at a
fixed point in the RAM and we know
how they're structured, it is easy to do a bit of RAM editing to set their health to zero. Here's two scripts that will set all of your Pokemon minus your starter's health to zero when you white out:
Here's for the Pokemon Centre:
And your mum:
To explain what's going on here; you're basically messing with your Pokemon's HP in the RAM. Those 'writebytetooffset' commands are overwriting your Pokemon's current health with zeroes. There are ten of these commands as each Pokemon's health takes up two bytes worth of space, accounting for Pokemon with more than 255 health. Since you're lengthening the healing scripts, they need to be repointed, which is taken care of with the little excerpts at the beginning of each script. Those static pointers at the beginning are where the scripts begin in the base ROM, but it a hassle to find and edit the pointers to those locations every single time, so I like to edit the healing scripts this way. This script should work regardless of whether you have one Pokemon or six.
Good luck with your hack~