I agree being a widow and being a lone parent is very hard work, it's the hardest thing I've ever done.
I don't think it's true though that you get dropped like a stone- or at least I haven't- my friends are my friends and that hasn't changed much, in fact, they were fantastic during those early days, but I think that's because they are strong friendships in their own right, and not dependent on being in a couple, I used to socialise separately from my husband and he had his own friends, and the couple side of thing we used to do with the odd BBQ or neighbours, but not to a great extent.
There are heaps and heaps of plus 40 women who are stuck with kids or older and want friends- my mum has been divorced and joined a walking group and choir, and I have a lot of friends through work.
I'm not saying it's easy, but I am saying it does reflect how you did friendships prior to the death- I think for the older generation in their 70's, then couple socializing was more common, but in my generation- I'm surprised it's that dominant. That said, many women are on their own as their husbands are not sociable, dead or left them so there are opportunities to add to the social circle if you want to, after the initial shock.