@NeedyLimeMember You have my sympathy, to be honest, and I entirely understand why you would want a day as a family over Christmas, rather than living for others.
It's all well and good saying this might be your MIL's last Christmas where she's functioning enough to resemble herself but I've always taken the view Christmas is more about children and, once they come along, the nuclear family (and focus) becomes the child(ren) and their parents.
How old are your children? You don't get many Christmases with them being young and, as parents, we often want to enjoy that time with them, in our own homes. I also think you're absolutely entitled to want a nice day, yourself, regardless of everything else. You absolutely matter! Some of the comments on here ultimately put your wants and needs to the bottom of the pile... Why?! It's a real MN approach, it seems, to diminish at OP to that rank.
That all said, I can understand your husband wanting the (possibly) "last" Christmas with his Mum. I also think it's worth bearing in mind the feelings afterwards if MIL does suddenly decline and you do or don't go to Christmas dinner with her e.g. relief / guilt. You don't want there to be a rift between you and your husband, in future.
I would, however, have a chat with him and cover the fact that this could go on for years so, while you're willing to do go this year, for that reason, it's not going to be a very positive way to approach Christmas every year until she's "gone". I'd have a plan for future years e.g. that you pick a different day to be with her to celebrate Christmas (it doesn't have to be when the rest of the family are there if it's really about spending time with MIL). I'd also make it clear to the rest of the family that your family's personal circumstances, this year, are that your husband is working 6/7 days over Christmas so you're not getting a single day as a family, with your children, at home - you're coming to be with MIL and see everyone but you need to cut the time down because Christmas Day needs to serve more than one purpose.
Finally, your husband can drive. Take a bottle of something you really enjoy and just indulge in it. If you're going to tell me you don't drink, I'd suggest you take it up (even if just for that day!).