Well, she might be right, though. I mean, yes, it'll be upsetting to your son, because he won't be used to it, but babies are resilient and if your partner steps up to the plate and is loving and caring with him, your son will be fine. It might be a struggle the first day, I'm not doubting it, but many have done it and come through it.
The only issue with weaning to me is, do you want to use expressed milk/formula for that period, or do you want to take the opportunity to move to formula generally? If the former, and I think that's actually what you want to do, then you'll need to express. Which yes, still means giving him a bottle, but isn't 'weaning'.
The issue isn't the weaning to a different substance. The issue is that you've been coping all alone for seven months, feel like there's no help, and that your son is entirely dependent on you and nobody else can now help. That's why I keep talking about the weaning issue. I think it's a red herring.
How does your partner see coping for the 48 hours in hospital part?