Extension of ISO vested options expiry date

I would like to understand implications of extending the expiry date of vested ISOPs beyond the plan expiry date for optionee and employer -

Optionee had vested options provided by the employer. Employer is a privately held company. Before the options expired, optionee, over email expressed to the CEO, Founder-Chairman, intentions to exercise all the vested options and requested for paperwork and guidance on the next steps. CEO emailed back to optionee explicitly stating that optionee's options stand extended for another 5 years and during this period they will continue to remain vested exercisable. 

Fast forwarding 2 year later, optionee continues to be the employee of the company. Founder-Chairman has brought new CEO who is rolling out a new ISOP plan with different terms and conditions than the previous plan. 

Questions seeking answers for -

1. What choices company has to make true to the promise previous CEO made to the optionee? 

2. In each of the choices what are the tax implications to the optionee? 

3. Optionee's preference is to exercise the options and would like company to issue the stock instead of any cash options. How does company fulfill this?