In PBEM campaigns, you
should have a "surrender or withdraw" option. Once you decide you need to give up, you retreat to your own baseline, and go onto the grey hexes to move your troops off-map.
Your opponent just may notice this, and try to stop you getting away with it thus necessitating some folks doing a delay mission as a rearguard (use support cannon fodder). And anyone left in a "kettle" might have some problems..
Once the enemy has taken all the objectives, and none of these are contested (no OK status troops within 500 metres AFAIR, and past the half way point), then the game
should fail the engagement check and end it there. Now - I have not tested that, but it should happen so. You could always set up a scratch test PBEM campaign and play it against yourself to check that it does in fact work. Let me know the results of your test battle(s) - if the game does
not terminate early then I'll need to check the end-of-battle code.
Assuming that it does work as I think it should, you have some options:
A surrender : You agree with your opponent that you will "run away, brave Sir Robin". He agrees not to interfere so that the termination happens reasonably quickly.
A withdrawal : You do
not tell your opponent about your "brave Sir Robin" manoeuvre
. Or you offer your surrender, but he decides to take no quarter and pursues you anyway
!.
A nasty : You offer to surrender and then when he accepts you fall back to reorganise and set up a counter ambush and smack him one. A "False white flag" situation. Don't expect any mercy in succeeding battles, though!.
Cheers
Andy