When someone lends you money and you do not pay back, the person can come and steal your money or force you to sell something from your membership, to pay the money back?
A debt from a loan may not be collected forcibly, only through the means of Bais Din. If one completely refuses to repay a loan, this is considered theft and at that point Bais Din will allow one to retrieve his money as he can.
Shulchan Aruch C:M 4:1,61:6. Ketzos Hachoshen 97:2. Imrei Binah, Tshuvos 3.