You can't really seize bitcoin. you can think you have. The only thing you need is a private key so if you store this in a encrypted file like you can with wallet.dat you can seize this file.

mean while you can have already split your key into parts and give them to trusted people. setup a dead man switch to email those people to talk and recombine private key, import into wallet and withdrawal funds.

this would have worked beautiful in silkroads case because the private was encrypted.