[cperciva]

I doubt investors would want to see the code they paid for released under a truly free license, since that would destroy any ability they might have to make money from it in the future. (Even if you're shutting down, they might fund another startup which they could sell the code to.)

However, you might be able to convince them to release the code under the GPL, since that leaves the option of dual licensing open -- in fact, you might be able to spin GPLing the code to your investors as a marketing tactic.