Keeping my last name

So I'm getting married to my favourite human in the world, which is great. But in the past when we talked hypothetically about marriage he would always say it would upset him if his wife didn't take his name. I never really thought I'd care about a name but now I'm starting to. The thing is my grandfather died recently and before he did, he expressed to my mum that the family name will die with him (as my uncle never had children, and all of my cousins changed their names when they were married). My mum then told him the name wouldn't die because I would keep it. I feel like now if I don't, I'm breaking her promise to him. But I also don't want to upset the man I'm planning my life with. Any advice? 🤔