Tanks and Mortars....Assault

[cjsiam]

So....T34s go into the trees after the Mortars....the T34s get demoralized (there was some bombardment)....

The T34s roll for recovery.....
They fail.....

Do they have to leave?  The Mortars do not have ability to hurt them (no AT) and they are in woods....
I'm a bit unsure as to what forces them to depart the hex---as it is there would be no free-shot (mortars don't get
  to free shot---their Assault DF is 1...for defense)...but do they have to flee?

I'm troubled---this happened a while ago in a game (to my dismay) --- and the latest assault question makes me want to clear this.
thanks!
cj