Here's an email I received in response to my question on this issue:

Hello Mr. Lorange,

Thank you for your e-mail.

The original bank of miles will be rolled into the new bank of miles
later this year. This will happen automatically. Once the miles are
rolled over they will have the same expiration policy as the new bank
of miles have. The expiration policy is the miles will not expire as
long as there is activity on your account once every 36 months.