EDIT: Ever since I've been coding when I check if a player exists I've always done it that way and I don't see any issues, unless you point some out.
I don't have the code. Is
%target referencing a player object, such as one you might get via
findClientByName(%serverCmdArgument).player?
I assume not, because
%target.player.kill("Self Delete"); // Slaying the target.
The problem with
if(!isObject(%target)) is that you are only checking if the
client exists. If the client is dead, either by getting ran over, ctrl+k, shot, whatever, then they do not have a player object.
Calling
%target.player.kill(); under those circumstances will result in an error about not being able to find object '' being dumped into the console. Not fatal, but not good coding practice either.