If nothing else, it seems to be easily scriptable (although please see the comments for warnings on a better approach):
bash/zsh: for pane in $(tmux list-panes -a -F "#D"); do tmux respawn-pane -k -t $pane; done
fish: for pane in (tmux list-panes -a -F "#D"); tmux respawn-pane -k -t $pane; end
As I'm sure you are aware, this should be used with caution since it will end any and all processes that are running in any of the other panes.