I realise this might sound a bit cruel to some, but part of me hopes that if they had filmed any Series 5 episodes, they don't show them. It would just be too painful to watch, knowing she died so shortly after.
I am tempted to say, they should use the filmed footage, to create a new storyline, of her death, maybe have just 1, 1 hour episode with Luke narrating his mothers final months.
That assume there is the kind of footage for that.
Even if S5 was finished, its not likely to be the right knid of ending, which may well be impossible now.
On the upside, they may have re-introduced Liz Shaw just in time, even if they only need her to finish one episode.