H1B Layoff will receive severance if till last day & transfer

[KR2021]

I am full time employee with a reputed American company. On 7th year of H1B (Valid till Oct 2021) with I140 approved in April 2014. 
Company is going to migrate IT systemt to another company , and is going to lay off the IT department. 
All the employees will get approximately 1 year of pay as severance , however only if they work till last day of migration. 
Last day of migration is not finalized and is tentatively Dec 2018 (5 Months) from now. 

So my question is : 
How should I time looking for the new job with dates not fixed for last day, I don't want to loose on severance as it is good amount of money.