Probably pretty high, but I never make promises I can't keep
But I have actually been thinking about these kinds of "problems", how to handle other people involved in projects in the best way?
1. Pay someone to do a certain amount of work as a freelancer? Good thing is you keep your potential earnings but the downside is the cost up front (and the potential zero income...).
2. Share revenue percentage once game is selling (if it is selling)? Hard part is to find someone willing to agree to this and also how is the percentages divided?
3. Start company together and share all burdens and profits equally?
4. Other solution? What have people here done? Kind of interested to know how the real world works.
When I was working in social gaming, I usually received a specific amount of cash per contract, plus royalties.
I'll give you an example.
I received a request to do music and sfx for a game. Usually I had to do 4 music tracks + all sfx (about 20 sounds, but don't ask me to do sfx, I usually hate to do that shit).
Let's assume we agreed on $1000. I receive $500 up front, then I get the rest when the job is done (usually in a week or two, sometimes in 2-3 days).
Then I receive a certain percentage off the money that is left after publishers get their cut.
The numbers are made up, of course, but you get the idea.
Also, the quality of work was questionable. It's hard for me to make the best shit non-stop. I usually need some time to experiment and find the right style for the project, and then I'm ready to produce cool stuff. Except I rarely had the time for that. Out of 6 projects I worked on during 2014, only one project allowed me to get the time in order to do some good stuff... but the funny part is, I got extra time because the programmer assigned to the project was a total hack, and they had to rewrite the code from scratch to make it work.
Then their next project was a complete disaster, and instead of giving it more time, they pushed the release date like a drinking party. After that I quit working for them.
If you ever encounter a noir detective game with oriental music, then it was probably me. Sorry about that.
EDIT: That doesn't mean I can only accept this kind of contracts. I'll tell you more when I'm not drunk.