I wouldn't do it, especially if you're looking to follow the law. If a corporation owned them and then went out of business, the rights don't just go away - the publishing rights belong to someone. By making molds of those old sculpts, you are infringing on someone's rights, and though the new owner may not choose to excercise those rights, they still have the say on whether the sculpt can be published again or not.
Ral Partha is a great example of this. After Ral Partha was sold to FASA in 1998, FASA had the rights to all of the Partha lines, but only kept Shadowrun stuff in production, and even that in limited numbers. The fantasy stuff was considered lost by many people. When FASA was, in turn, bought by Wizards of the Coast in 2000, Wizards decided to put some of the original Partha sculpts back into production through their new subsidiary Iron Wind Metals. This was possible because those old OOP figures were still owned, and eventually put back into production when the money was right.
Here's something to consider as well when making your decision: IWM only started off producing a very limited number of classic best-sellers, to see if there was a market. There was, and now most of the old Partha stuff is available again, including many of the Shadowrun sculpts that I personally love. If many folks had written Partha off and made their own copies, there would have been no financial incentive to put those figures back into production, and it would actually have made it harder for us to get access to the whole range again.
Sorry for the long post, but this is something that's near to my heart.
