What actually has a fixed expiry date is childhood. Your MIL might live another 5-10+ years, your children won't be the same and you won't be able to go back and make those memories.
You need to say to your husband that you would like to enjoy at least a 1-2 week holiday each year with just you as a family. The ages that your children are is precious, fleeting and you want to make lasting family memories without your MIL (and presumably the limitations brought by her age).
If your husband wants to prioritise his sporting event and his mother over this perfectly reasonable request, tell him frankly that he is damaging his marriage. You have the option, if he won't budge, to say that you simply aren't going on the holiday with MIL, as you would rather holiday by yourself with the children, like a separated couple. Obviously, only say this if it is what you would genuinely prefer (I wouldn't blame you!).
You can sympathise with his feelings about his mother, but they can't be allowed to unilaterally determine the parameters of your family life.
Don't make it about your MIL. This isn't about avoiding holidaying with her, but rather it's about making time for a holiday that's just with your husband and kids. It's then your husband's job to sort out other opportunities for holidaying with her.
Ideally he would also take her up on rude comments about your weight etc(!) but it's probably better to cross one bridge at a time...