If my airline is on strike and is not able to reaccommodate me on a partner airline, can I purchase my own ticket on another airline and expect the original airline to reimburse me?

There are no provisions guaranteeing you anything in the case of a labor disruption. That being said, airlines will nearly always try to help their passengers. In many instances the automatic response is to book passengers on the next available flight on the same airline and waive the change fees. The
airlines may also offer some or all of the following options depending on circumstances:

• If the strike affects all flights –
  Rebook you on an available partner airline flight at no additional cost
• If the strike is prolonged and there are no available partner airline flights –
  Rebook you on an available flight on a non-partner airline at no additional cost
• If your dates are flexible –
  Rebook you for later travel dates at no additional cost
• If cancelling your trip is the best option for you –
  Provide a full refund with no penalties

Avoid the temptation to book your own flight on another airline expecting the original airline to reimburse you. The striking airline must be the one to handle the rebooking.”