Sure. Rules are totally separate from the interface config. After all, firewalls can have routers behind them.
In general, you should remove the interface from the topology table in the firewall object on the management server, push policy, then remove the interface config on the firewalls themselves. That way, the firewall software stops looking for the interface before the interface actually goes away. If you remove the interface on the CLI first, you could get failovers and other weird behavior because the firewall software may still be trying to use it.