Personally, when companies (or movies, or albums, or books, or games, etc.) become worth enormous amounts of money I think there should be bonus royalties for everyone involved even if they sold their labor for a flat rate.
No, I don't have a good plan for how you'd calculate the distribution. But it would make windfalls more fair to the people that made them happen. And that kind of mechanism could also help fund many open source projects.
You can just add this to your contract if you think there's a good shot at success.
Apparently, in this case, the license _did_ in fact forbid this usage, which is why they changed logo in the first place: https://en.wikipedia.org/wiki/Simon_Oxley#Twitter_Bird_Logo_...
No one wants to deal with a 0.0001% or 0.00001% royalty clause in an individual contact.
Ah, come to France, maybe that explains my "sure of myself" answer in the parent comment. 0.0*01% + "à-valoir" is very common and cover the situation described here (eg you get paid a paid royalty, in advance, if the revenue ever exceed you are owed it, but if it's always under you never have to pay back).
Sort of a "I pay you 100€ but if this turns out to be a billion euro thing you get you gold ticket too".
You can also be a generous person, and share a few pennies from your pocket.