If the Whonix-Workstation was compromised an adversary would have access to all your data However, all network traffic would still be forced over Tor by Whonix-Gateway including any efforts by a “phone home virus”.
There would be some advantage in physical isolation but only if you’re an advanced user that can troubleshoot any problems that might come up.
Keep in mind you should not decide on which Whonix Variant to use based on one specific attack vector. Qubes-Whonix provides the best combination of security And usability. But if you are interested in physical isolation Qubes-Whonix style it would be a good idea to first use Qubes-Whonix without physical isolation for a while first.
There is a saying. “You have to learn the trade before you learnt the tricks of the trade” applies here.