The answer is "it depends."
For example, my 1100 cannot be used even as a firewall after Jun 12th unless I get a new license for it
However, my 1490 clearly could:
My guess is that your 600 is provisioned with a different SKU that results in a Firewall license that expires, similar to my 1100 above.
(My 1100 is a pre-production unit)
In theory, all appliances should include a license for Firewall + VPN that doesn't expire.
Either way, I would check with Account Services.
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