My understanding is that Freo need to put through their next "list disclosure" by Monday, so yes, Clarke could walk if he is not contracted. I believe player contracts end 31st October, so if he is unsigned, then...
The following is from Gestapo Propaganda HQ (AFL website)
Delisted players become free agents and can join new clubs during any of the three NAB AFL delisted player free agency windows.
Once clubs have delisted a player, they will receive no compensation should that player be signed by a new club.
The key dates for delisted free agents are as follows:
Tuesday November 1 - NAB AFL delisted player free agency period (1) begins
Tuesday November 8 - NAB AFL delisted player free agency period (1) closes
Thursday November 10 - NAB AFL delisted player free agency period (2) begins
Friday November 18 - NAB AFL delisted player free agency period (2) closes
Saturday November 26 - NAB AFL delisted player free agency period (3) begins
Sunday November 27, 2pm - NAB AFL delisted player free agency period (3) closes
Monday November 30, 2pm - Final AFL club list lodgement
Delisted players can also nominate for the NAB AFL Pre-Season Draft.