You can check your Memory-Map subscription expiry date using the Memory-Map Licence Management System. This is accessed by pressing the 'SIGN-IN' option on the Memory-Map website and signing into your account.
Once you are signed in press Activity > Purchases and you will see a list of all the Memory-Map licence managed purchases you have made, including any subscription purchases.....
Press Maps and you will see a list of the licence managed maps registered to your account including all of the maps included in your subscription. This shows you how many devices you can have the map on and on which date the subscription will expire: