hai caroline,
You don’t need to re-create your send and receive ports.
Step 1:
When you want to undeploy a assembly, you just supprime the name of maps in send and receive ports .
Step 2:
Undeploy the assembly(Now it will undeploy the assembly successfully)
Step 3:
If you want to redeploy it,Change the version of your biztalk project as 1.0.0.1 and deploy.
Step 4:
Add the name of map in the already existing send and receive ports and test.
I hope this helps you.If want further details write me again