When you say "cluster link" I assume you mean the sync network between the cluster members. If that link is unplugged the State Sync pnote will fail indicating an impairment on both members. Assuming the members can still see each other's CCP traffic through at least one other clustered interface, the members will not split-brain in this case and whichever firewall was Active will continue to pass traffic but in Active Attention (!) mode. I think the standby member will show a Down state, but will immediately go Active Attention (!) if something happens to the currently-active member. This all assumes that the cluster was in a proper Active/Standby state to begin with and there are no other pnote failures.
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