A way to prolong your selling season is to make a special offer to your best customers this or next week, before the end of the year.
You'll want to target the best customers (what I call the VIPs and Loyals in Repeat Customer Insights).
You'll want to give them a short-time coupon or free gift on their next order.
You can call it a VIP perk or a reward for their loyalty over the year.
You could also send something to your potentially loyal customers. These customers are the ones who are showing some loyal behavior but aren't quite there yet. Either they don't have enough order history or aren't ordering as often as the VIPs.
Convince them to become loyal and you might be able to influence their purchases next year.
Analyze your customer's behaviors before they defect
Your customers aren't yours forever. Some might have defected today, never to be seen again.
You need to analyze your customer behavior so you can reach them before they defect.