If you need more than the basic app available for free, purchase the Locus Map Premium Voucher.
Google Play Store is now necessary only for processing the subscription. The Premium is associated with your Locus account that you are logged in during the Premium purchase.
So, when you uninstall the Google Play Store and services after the Premium purchase, you can go on using the Premium version with all its features.
When you purchase Premium on one phone with Google Play and then you install Locus Map on another device without Google, log in to your Locus account the same way you used during the purchase on the first phone - you'll get all your Premium features there too!