[wiredd]

That depends on vesting. You own whatever portion of the 35% that has vested based on your contract and have legal rights to it, although your contract could have repurchase clauses that allow the company to buy back shares at a price you may not like. Vesting clauses are common for cofounders as well as employees, and this is usually a good thing to avoid the possibility of a cofounder working for a couple of months and then leaving with full ownership.

[jamesaguilar]

Sure, I guess the circumstance that would concern me is if I worked for years.

[manuelflara]

Then there's nothing to worry about (if proper vesting clauses are in place), since you'll have vested (and thus, would keep on your way out) the proper amount of your 35%.