There is no builtin way to do this but it seems like it would be trivial to write a script to save all the buffers every few minutes and reload them when you start the server, something like (to save):
mkdir -p ~/.tmux.d/buffers ~/.tmux.d/buffers.old
rm -f ~/.tmux.d/buffers.old/*
mv ~/.tmux.d/buffers/* ~/.tmux.d/buffers.old
tmux lsb -F '#{buffer_name}'|while read n; do
tmux saveb -b $n ~/.tmux.d/buffers/$n
done
And to reload:
for n in ~/.tmux.d/buffers/*; do
case $n in
buffer*)
tmux loadb $n
;;
*)
tmux loadb -b $(basename $n) $n
;;
esac
done
This may need some tweaks to load automatic buffers in the right order (maybe put #{buffer_created} in the name and sort by that?).