Great question! The stay would need to be completed within 1 year. Hotels will not be able to apply the certificate to a stay in their system once it has expired.
What is this Travel Package you are discussing? Is it a promotion on Marriott? I'm already at Companion Pass status for 2017 w/ SW. But didn't know if I should find out more... I have some friends that are not at Companion Pass status w/ SW and this could be something their interested in. Thank for any information that can be shared.
Link above. I used 300k Marriott points for 7 night category 6 certificate and 120k southwest points. My SW companion posted today.
Note that SW will only allow this to qualify for companion pass until 3/31.