pfSense

Disabling the parent interface will stop the connectivity to all connected networks/VLANs , the vlan is up and you can ping the vlan interface inside pfsense but it will not be able to communicate.

I can ping the vlan interface 10.100.100.1 when the parent interface is down :

C:\Users\I>ping 10.100.100.1 -t

Pinging 10.100.100.1 with 32 bytes of data:
Reply from 10.100.100.1: bytes=32 time=21ms TTL=64
Reply from 10.100.100.1: bytes=32 time=3ms TTL=64
Reply from 10.100.100.1: bytes=32 time=6ms TTL=64

while the client 10.100.100.100 in same vlan is not reachable:

C:\Users\I>ping 10.100.100.100 -t

Pinging 10.100.100.100 with 32 bytes of data:
Reply from 192.168.254.200: Destination host unreachable.
Reply from 192.168.254.200: Destination host unreachable.
Reply from 192.168.254.200: Destination host unreachable.
Reply from 192.168.254.200: Destination host unreachable.

this is a normal behavior in most Switches/Routers .