There are so many instances of paths just 'disappearing'.
But, once a highway always a highway, unless formally closed or diverted!
Locally there was a similar situation. A new house was built filling in a gap, and the path went down one side of the plot of land. The line of the path was not built on so theoretically the path now goes down the side of the house, through the back garden and exits into a field. I raised the matter with the county council, before the house was finished, and they did at least send someone out to offer advice to the builder/purchaser. I don't know if the path is still usable but I always feel uncomfortable using such paths, even though I am in my rights to do so. There is a reasonably convenient alternative which joins up with the path mentioned.
Part of the problem is if you have district councils (who deal with most planning applications) and county councils (who deal with rights of way). I cannot recall one but it must have happened somewhere where the applicant or planner states 'this development
will (rather than
may) affect a right of way', or where a county council submit an objection to a planning application because it affects a right of way.
Then it depends on the attitude of the council, some are more active than others at protecting and restoring routes. Even before 'austerity' some councils were pretty lack-lustre.
In the parish adjacent to me, there is a parish council but it does not have a rights of way sub-committee so there is no-one on the ground locally chasing things up. There were two paths through the garden of a bungalow, where the county council wouldn't do anything because the owner was ill (unspecified and none of my business). After several years the person died and the purchaser (or seller) of the bungalow wanted the matter resolving. The paths were diverted away from the garden. Simple enough but why couldn't that have been done sooner?
In the same village a large bungalow with spacious garden was built in the 1970's and room could easily have been left for the path. The response I got to that one was that 'the legal department are aware of it', not dealing with it mind you, even 15 years after I submitted the obstruction form. And so on.
There never seems to be any progress on dealing with the list of 'claimed paths' even before the deadline and The Ramblers campaign to log as many as possible. Having looked at The Ramblers website last night there are some not shown which have previously been claimed and remain unresolved to my knowledge.
Link to don't lose you way page, requires registration.