I stumbled on the story below, shown on the link. I pasted part of it, which pretty much sums up the whole story. The link or story is too long. I read only part of it, but the link there if you or your sister wants to see what her future will be like without him.
- My spouse/partner filled more than just one role in my life. Losing even “just” one person in our life is hard enough. But following the loss of a spouse or partner, a griever will feel like they’ve lost many important people: their friend, their lover, their peer, their co-parent, their confidant, their business partner, their travel companion, their date…meaning that this loss doesn’t mean the loss of “just” one person. This loss will create a vacancy in many roles that one very important person had previously filled. And no one person is going to be able to take the place of all the roles a spouse or partner filled.
the woman who described the feeling of shared investment that she had lost when her husband died. She told me that the slow recognition of this fact was actually a huge turning point for her. Because when she started to take a look at all the reasons that she was struggling and all the reasons she missed her husband it revealed something even more important: all the things they had shared together. And lying underneath the sadness and yearning for what she had, was a realization of the blessings that their union and time together had created.
https://www.griefincommon.com/blog/loss-of-a-spouse-5-things-only-a-widow-understands/