Co-founder equity situation - early stage startup exit scenarios

Currently CTO/co-founder of early-stage US startup. Just me and CEO, with launched product generating revenue (covers costs + small reserves). I handle all development, we split expenses equally, I have slightly less equity.

Considering departure due to personal circumstances. Company has no formal valuation or outside investment.

Questions for the community:

What typically happens to co-founder equity in early-stage exits? Has anyone experienced similar situations where a technical co-founder left before any formal valuation/investment rounds?

Curious about standard industry practices and what others have encountered.