Yes I remember the horror of your half term very well - I felt so desperately sad for all of you. You mentioned then, I think, that you might need to give up work in order to be available to care for the GC, but now, it seems, your DiL's family are mostly taking over that role, so although you do some of the childcare this hasn't stopped you from continuing to work.
For what it's worth, I would say carry on as you are for the moment. As pensionpat says, now is not the time for big decisions. Nor is it the time for making such a major change to your life. Your world has been turned upside down by your DiL's diagnosis and if there's one thing you need it's to hang onto something that provides you with a sense of continuing normality - your work routine and the pressures of working will force you, if only momentarily, to put your worries out of your mind. And your colleagues will be there as an impartial support outside of the family, which is so important. You recognise that your DS may need 'a place to come to get away from the trauma for a few hours'. You need this too.
So carry on working for a while, and use the money to replace all your white goods while you can, and get your house redecorated. Then when you do retire you won't have those expenses to worry about on top of other concerns.
Good luck, and I so hope things turn out a little better for your family, particularly that your dear DiL responds well to treatment and is relieved of her pain. 