I’m one who has been there. Lost my wife of 24 years in 1996, following a fast-acting (just over a year) dementing illness.
At age 47, with two children (age 19 and 13) it was devastating. But as Nevermind correctly pointed out, I had some time to prepare for it. (I thought I had, maybe, another year to go, but at the time she was bedridden and nonverbal, so much of her was gone already).
It was a couple of weeks later that it came to me that I was allowed to think about the possibility of dating other women, that it was OK with society. A very strange feeling, because we were of the very married sort. It was something that was settled – we had found life partners and that, I thought, was that.
I eventually began dating five or six months after her death, a lady I had known 30 years earlier. We decided to marry a few months later, but waited until a year and two months since my first wife’s death to announce it to our families. We were married just under two years after the death, and have been extremely happy since (coming up on 4 years this fall).
One thing I have read in the literature about widows and widowers, and it is absolutely true – the better your marriage, the quicker you will feel like remarrying.
I have been lucky enough to strike it rich twice, but that may not be the case for all.
I will say that my daughter, who was 20 at the time we announced our engagement, was upset. My son, then 14, was a bit more resiliant. In the time since, they both have come to love her, and I have come to admire her grown daughter as well.
It’s always dangerous to project from a sample size of one, but I can say that the possibility exists for your dad to be as lucky as I have been.
Hope that helps