How could that occur? It will continue to cost significant sums of money year on year, for maintenance, admin, security and the like. Contracts of hundreds of millions for support are already in place (some with companies like Hinduja Global Solutions, a subsidiary of an Indian conglomerate - no issues with data security there).
The cost of the system is estimated at £2bn. If it comes in at anything less than £15bn I'll post a video on this forum of me eating my hat.
There are no savings to be made anywhere. People will still need passports and driving licences. This will cost a fortune and offer next to no benefit for individual citizens.