I'd agree - your first port of call should be to check whatever agreements are in place around the options. However, it is highly unlikely you will be able to get anything of value if you leave. The whole point of options is to attract and more importantly retain good people. In most cases, if you leave you leave any value attached to options or shares is left behind. This is especially true if there is no market in the shares, as would be the case in most startups. In fact, until there is some form of exit event (e.g. floatation or trade sale) it is rare that anyone will get any real (as opposed to notional) return on options or indeed shares. Another scenario is where you exercise the option and get shares which are subsequently wiped out in a funding round. The rules and agreements around the option scheme should explain it all, though.