Hopefully you guys are using source control. If you demonstrate that the commit history has no commits made by this person, it might be a pretty good argument that no measurable work has been done by this person. IANAL, so I don't know if this has any legal weight behind it, though.

Not necessarily.

The usage of source control does not demonstrate the lack of effort, it only demonstrates effort.

One could argue that effort has been put elsewhere and was simply not committed (and may rightfully do so under certain circumstances).

I don't believe Source Versioning logs would be much of an 'exhibit' or even receivable in a court of law.

Then again, the idea is to break the case ahead, so it could be used to dissuade said partner to go any further in any proceedings.

I don't believe Source Versioning logs would be much of an 'exhibit' or even receivable in a court of law.

Sure it is.

Same with the emails discussed earlier.

Their usefulness would depend on whatever the case is, what they are trying to show.

If they are trying to show that there was an agreement that they get a particular share of the business, email or text messages could show there are agreements in place even if nothing was ever signed.

Email communications can show that they had reached an agreement or not reached an agreement. Even if it is not a lawyer-drafted contract, if they reached an agreement about what would be paid and on what conditions it would be paid, and the other people accepted the agreement, that written agreement is legally binding.

Email communications and text messages can show that a person was doing work, document that a person was complimented on the work. They can document a pattern of being told they are not working, or are not doing as much as they are expected, or that the work they are contributing is not up to par.

Source control could show that a person contributed, what they contributed, and how frequently they contributed it. It could also be used to show they did not contribute regularly to the main line but that other people with the same position and the same expectations contributed frequently. In a court case, the person would need to explain why they did not contribute regularly to the source control when their peers were contributing frequently. If they could justify a lack of contributions directly and easily that might work, but if they struggled or presented a weak explanation the version control logs could be quite condemning.

Source control could show that a person contributed, what they contributed, and how frequently they contributed it. It could also be used to show they did not contribute regularly to the main line but that other people with the same position and the same expectations contributed frequently. In a court case, the person would need to explain why they did not contribute regularly to the source control when their peers were contributing frequently. If they could justify a lack of contributions directly and easily thaTht might work, but if they struggled or presented a weak explanation the version control logs could be quite condemning.

That's assuming that contributing a meaningful amount of works equates using source control to begin with.

One might argue that work was made, and delivered in an alternate and less efficient way (.zip) and that said file can't be presented for x,y reason.

Now, obviously, it depends solely on who is starting these proceedings, as it will be effectively be this party's role to prove the existence or lack of existence of such files.

In the OP's position, trying to prove the inexistence of work would be pretty difficult, meaning attempting a lawsuit against their former partner would most likely be a defunct cause, but, it would also likely be a great defence as they are not likely to attempt a lawsuit on them, as it will be equally difficult to prove the existence of such work (assuming that, as the OP stated, such work does NOT exist). I imagine the former partner's case would be the existence of a written clause (emails only) that stipulates they are entitled shares in the project, and the defendant's case would be that these shares are dependant on proof of fair contribution to the project, at which point the pursuant may be prompted to establish their claim by providing exhibit of their contribution, and have this examined by an expert witness if it even reaches that far.

Chances are though, none of this ever happens.