What if my co-founder leaves?

Today: protect access

• Do not delete or lock anything. Write down what you can still reach and what you cannot.
• Make sure at least two people hold full control of the domain, GitHub organisation, hosting, Meta business portfolio, LinkedIn Page and payments. Add yourself first if you can.
• Change passwords and 2FA only on accounts that are yours or the project's. Do not log in to accounts you have no right to use.
• Check the cards attached to ad accounts and subscriptions and who can change them.

This week: save the evidence

• Screenshot the member and admin lists of each tool, with dates.
• Export what you can: repo clones, customer lists, analytics, ad reports, invoices.
• Save emails, chats and commits that show who agreed what and who did what.
• If you used a ledger or founder record, download the latest version.

Then: agree the exit in writing

• Write down each person's share, what they keep and what they hand over.
• List every account they control and a handover date for each.
• Agree who pays what until the handover is done.
• Put it in a short signed agreement. Have a lawyer check it if real money or customers are involved.

After: close the gaps

• Remove the leaver's access only after the new admin is in place.
• Rotate keys, tokens and environment secrets they could see.
• Move recovery emails and phone numbers to project-owned ones.
• Settle up shared costs to the leaving date and update the record of who owns what.

I am a co-founder of a small project and the situation with my co-founder has gone wrong. I am not a lawyer and want a practical plan, not legal advice.
What happened: [DESCRIBE IN A FEW SENTENCES].
Country: [COUNTRY]. Do we have a company? [YES/NO]. Is there a written agreement? [YES/NO].
What I still control: [LIST ACCOUNTS]. What I lost access to: [LIST ACCOUNTS].
Please give me: 1) the five most urgent things to do in the next 48 hours, 2) what evidence to save and how, 3) a calm, factual first message to my co-founder asking for a handover with a deadline, 4) questions to ask a lawyer.
Do not suggest breaking into any account.