I am not exactly sure what you're asking and if it's even a question for Plesk staff to answer.
Even though WPB isn't being actively developed any more and there are newer web build tools (e.a Sitejet) available, it's still supported by Plesk and can still be installed and used on the most recent Plesk versions. That being said, WPB has been outdated for quite some time and lacks modern features. So It would not be my recommendation if you like to create a new website. But maintaining an existing WPB website it should do just fine.
From your initial post I take it that your not running your own server with Plesk, but rather are hosting your website(s) with a hosting provider that offers WPB. And I assume, based on your questions, that they might stop to offer WPB or your not quite happy with your provider, and thus are searching for an alternative. In which case the alternatives I can think of are:
- Find that hosting provider that does still offer WPB
This might a challenge, as WPB is rather outdated and there are new/better tools available to hosting providers can offer to their customers.
- Run your own server with Plesk and WPB
Running your own server gives you the benefit of customizing your server and hosting environment to your own specific needs. If you're not comfortable running and managing your own server, find a provider who provides "managed" (virtual) servers with Plesk for you.
- Rebuild your website(s) on a different platform/cms.
Cut your ties to WPB and rebuild your website(s) with/on a modern platform or CMS (like Wordpress for example). If you lack the skills to rebuild the websites yourself, find a developer in your area or use a platform like Fiverr to find a developer within your budget.
Hope this helps and answers your questions at least some what.