Sybase doesn't allow a nullable ID column in a M:N relation table. In Order.hbm.xml, the 'orderContacts' set is defined without a not-null constraint on the order_id column.
This causes the DDL to not generate properly - the table t_order_orderContacts will not be created:

ERROR SchemaExport:483 - HHH000389: Unsuccessful: create table t_order_orderContacts (order_id int null, elt int not null, primary key (order_id, elt)) lock datarows
ERROR SchemaExport:484 - Column 'order_id' is part of a primary key constraint and cannot be null.

When dropping the schema, Hibernate attempts to drop constraints from the inverse side:

 alter table order_contact_orders 
             drop constraint FK96fm4tqlfxts86uxuuhu19uci

But this query will hang forever due to not existing t_order_orderContacts.