My hammy died, how do they go from being good to gone so quickly?

I adopted a robo hamster a few months ago. She was good on Saturday night. She woke and rambled around a few times on Sunday. She didn't wake late Sunday night as per usual. Some more hours passed and still didn't get up. I thought she was sleeping.

I went to check on her and she was curled up in her favourite place, in her sandbath. I thought she was still asleep or maybe she was injured. But she didn't wake. There wasn't any movement from her.

I held her, all night.

How do they go from being good with plenty of activity to being gone?

I ordered hamster supplies last week and they were delivered today.

What do I do with them now. Do I hold onto them for my next hamster but I am not able to get another jet. It will be a few months. Or I know a girl with a hamster. Do I give them away.