Why not? They'd have freedom to do what they want and all the money would go to them.
This is wrong.
Volition is a wholly-owned subsidiary of THQ. As such, they are not free to make their own business decisions, everything they do has to be signed off (and ultimately financed) by THQ. Going indie is only a good idea if
can prove to THQ's management (and the bankruptcy administrators!) that they can turn a healthy profit by doing so; Considering that any such move would mean abandoning or delaying projects that are assumed to be very profitable indeed (namely Saint's Row 4), noone in their right minds would support such a notion.
Now, that does not mean that they can't do what Obsidian did and do a Kickstarter-funded project (Or go the Star Citizen route of using crowdfunding to get other investors on board), but it's somewhat unlikely for them to take such a leap of confidence when they can just as well continue what they have been doing and have a somewhat sure way of generating revenue.