It's not possible to disable a static route that is set to use a gateway that is disabled using the edit dialogue.
If you attempt to edit a static route to disable it and the gateway set is already disabled you will receive the following:
The following input errors were detected:
The gateway '192.168.114.22' is a different Address Family as network '192.168.119.0'.
It can be disabled using the enable/disable button on the System > Routing, Routes tab.
Related to this. If you are disabling a route and gateway and first disable and save route then disable and save the gateway then apply the changes, the route is not removed from the system routing table.