My husbands father has dementia, he recently lost his wife and is dealing with depression. How can we help him get through it?

My mother-in-law had the beginnings of dementia when her husband died. It threw her full steam into dementia further with the stress of his illness and subsequent death. Her short term memory took the brunt of it, so I understand a little as to what your father-in-law is going through. He has got to have time to mourn his loss, regardless of his mental state. He is going to feel depressed for awhile, and you can't just keep him busy in hopes he won't be lonely. We tried to keep my mother-in-law busy with family because we also felt guilty that she was home alone in her grief. But she was going to grieve whether we kept her busy or not, it's just the way it is. She also was put on a mild anti-depressant for maybe 6 months but her doctor said it was only temporary because it was natural to be depressed after losing her husband of 60 years.
So give him time, love him, and you can still take him places to get his mind off his loss temporarily. But at night when he's laying in bed alone, there's nothing you can do.