New member question

[19 Delta]

Hi, I recently purchased PzB Normandy and have a quick question . After doing some searching I found there isnt a offical game forum to ask questions on but luckily found this forum which seems from what I have read is very knowledgeable on the title .... 

My question is about unit casualties and its effects on ability to engage.  After a few battles I noticed even units that have more then three quarters of their numbers reduced are still eager to engage?  .... I find this odd , I have looked in the manual and found nothing on what it takes to rout a unit due to casualties.