When I was working full time as a freelance illustrator, I had to work my arse off constantly on other people's IP just to scrape by. I was able to pay my rent, but even buying myself like... one video game or a new pair of pants was an extravagance, and I never got to draw anything for myself based on my own IP. That was while earning what was, according to a recent study, about twice what an average illustrator in my country earns. It's not fun being a "starving artist", and it definitely doesn't spark creativity or better work for me.
So with that in mind, of COURSE I would take somebody up on it if they offered me £2 million for just one of my ideas. Even I'm not egotistical enough to think that any of my comics are some kind of high literature that must have their artistic integrity protected. They're cheap entertainment that will probably not age well so like... yeah, whatever!
Not only would I be free from financial burdens and able to work on whatever the hell I want, but the other thing is, once you've managed to make a big sell like that and the adaptation is out there and known, publishers are all suddenly VERY keen to take pitches from you and let you do whatever you want. Like even if your ideas are bloody awful and the one that got popular was your one good idea, or the only reason the work you're known for actually made money was the work of the person adapting it making it good, as far as publishers and the press are concerned, you're a person who comes up with million dollar ideas and should be given artistic freedom to make stuff with a meaty advance and a publishing deal because even if the next idea is crap, it'll still probably break even based on your name and visibility alone. If you have a reputation like that, you can make stuff that if you pitched it normally you'd just get completely ignored. You think Alan Moore could have got something as weird as "Alice in Sunderland" published and have it make sales if he wasn't already a hugely popular comics writer? or That Bryan Lee O'Malley's "Seconds" would have been more than a forgotten random self-published indie comic lucky to be picked up by anyone if he hadn't already hit it big with Scott Pilgrim?
So yeah, as much as it might suck to sell something I really love, like Errant, what it'd buy me would be freedom to be financially secure while making whatever the hell I want for the rest of my life.