Proposals already have an expiration date. So they should have no need to be included here. Can see them being counted down by days.
However Proxies to another account should also expire. Not much point to an expiry to the witness if proxies still stand.

For the first term of the change . Adding the expiration. This should be a period of no longer than 3 months. Shorter if possible. After that first vote of 3 month a term of 1 year can be implemented.

Notification to an account that its vote will expire in one month is enough. Adding a decay to that is ridiculous and just adds to code needing to be wrote.