They can be classed as an asset and as such the Administrator can seize them and sell them off to repay Creditors.
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It also depends I think on whether you mean the client declared personal bankruptcy or if his ltd company went bankrupt and which identity owns/is registrar of the domains.
Do they owe you money for your services? If so, put in a claim against them maybe.
Theres a few niches that he couldnt work in...certain financial ones, security, but on most occasions you can appeal and get an exemption because it tends to intrude on "restraint of trade" and ones right to earn an income. There is and can be legal ways around the income situation.but it seems based on other info i have he can't trade in the same business sector for 5 years or so.
If they are decent domains you could always make a low ball offer to the administrator (as someone that has invested a bit of time in them) and see what they say....with a bit of luck they may not be so 'up to date' on the ins and outs of trading au domains.