If they open source it, who cares? Obviously I would like them to continue maintaining their stuff, and I am sure they are imaginative enough to find some source of income.
They only try to create enough value that the VC can one day sell their stake for more than they paid for it. The key is convincing the VC not that that is particularly likely, but that if it happens there's a chance it'll be a lot more than they paid for it.
[0] occasionally a company gives money back to investors when it fails
Honest question - have you worked with VC’s much? That’s pretty much the MO. Get a snippet of an idea that has the potential to scale to unicorn levels, make sure you have a super coarse idea of how to monetise it, and then shoot and see how far you get.
