Fortigate dual internet & policy routes question

I have a Fortigate and configured 2 interfaces that connect to 2 different ISPs.

Interface 9 - ISP A

Interface 10 - ISP B

Basically, I would like all computers to use interface 9, except for a selected few that will use interface 10.

Interface 10 is configured with a DHCP, and I've been told that because of this, Interface 10 becomes the default route. To fix this, I created a Policy Route so that all traffic goes to Interface 9. Then I created another  Policy Route to make the selected few computers to use Interface 10. This all works perfectly fine.

My question is: If interface 9 goes down, will the computers automatically use Interface 10?

I don't want it to use interface 10, I want the computers to just not have any internet access at all if interface 9 is down. (sounds odd but there's a reason for that). I am unable to test this out now, hence this question.