Is there a way to extend or stop the expiration limit of Offline Maps provided in Google Maps? I was wondering if there's a way to either completely turn off or extend the time frame of expiration for Google Maps - Offline feature.

I tried to search about it, but almost all blogs suggests that these offline stored maps expire in 30 days. The notification for their expiration reads "Offline maps expiring  You won't be able to use them after they expire."

Now, this a little too frequent and I'm unable to access the Stored Maps (without internet) post this time frame without an update.
Unfortunately it's not possible.

Straight from the horse's mouth:


  Offline areas that you downloaded on your phone or tablet need to be
  updated at least every 30 days.
  
  If your offline area expires in 15 days or less, Google Maps will try
  to update your area when you're connected to the Internet and plugged
  into a charger.


(from Google Maps Help - Download areas and navigate offline)

There's a bit of conjecture online about what the reason for this may be, and whether it's potentially related to Google being worried that maps will be out of date. On the same link above, I would say this gives a clue:


  Note: Downloading offline areas isn't available in some regions
  because of contractual limitations, language support, address formats,
  or other reasons.


Although there's no official word from Google on it, I'd say it's highly likely that this time limit is related to contractual limitations at least in some areas. Kindof like how iTunes rentals expire, or Spotify Premium offline playlists expire: if there was no expiry date at all, then there's no difference between 'accessing' and effectively 'permanently buying for free/cheap'.

If offline maps are very important to you, you may want to consider apps that support OpenStreetMap (or see this answer).