For me it doesnt matter if they are partners or not, if he is bailing out of the project he cant have the right to ask for money on the project
This whole matter of rights is easy to explain:
Javier is a co-founder of Red Lolly, at least that's what he reflects on his social networks and that's what they implied in his presentation on Patreon, therefore a percentage of the company is his. If Javier leaves the project, he has three options: just give his part to his partner, sell that part to her, or ask for a percentage of the monthly profits. But his part of the company is entirely his and, therefore, he has complete rights over it.
Assuming they work as a company. If not, if they are simply friends who wanted to do a project together, then each one owns the part that he has done and, therefore, if they break up, each one takes his part and that's it. It is like, for example, if in a relationship with your girlfriend you buy the car. You both use it, she often uses it to go to work but in return she always pays gas and taxes, etc... If the relationship breaks down, the car remains yours, you have every right to take the car, but, since your now ex-girlfriend needs it more than you do, you agree to sell it to her or she pays you a small monthly rent to use it.
It's a very different case when you're an employee or a freelancer doing commissioned work for a company. Usually they make you sign a document that you agree to assign in perpetuity the copyright of commercial use of the material you make for them, you agree to resign your copyright forever. So if you make them an illustration, they pay you what was agreed and that's it, you can't claim anything in the future because you've signed a rights assignment contract.