I did fear that when the BA lounge in Belfast was handed over to Aspire to become a third party lounge around six months ago, that it would not be the only domestic route to lose a dedicated BA lounge. It is very disappointing to hear that Newcastle is next. I do fear for the long term future of the remaining domestic lounges outside of London. Manchester in particular must be at risk,
I wonder if it is possible that it could be taken over by Aspire as in Belfast, and open to more than just BA passengers. It has been a while since I've been in Newcastle, so I may have remembered incorrectly, but from what I recall to get to the BA lounge you had to pass through door to go down a corridor, after which you couldn't return to the main terminal. If that is the case, it doesn't make it a great location for a third party lounge open to all.
The Aspire Lounge at Newcastle isn't that big from what I remember and has always been quite busy anytime I've been there, so I would imagine it would struggle with space if the BA passengers were accommodated there too. I haven't seen the Aspire Plus side of the lounge though, so maybe BA would do a deal to accommodate passengers there if the existing BA lounge space doesn't become a third party lounge.