Now that I’ve got a free moment I’m going to try to cut through the bickering and summarize the information that’s responsive to the OP:
Can an unwitnessed will be valid?
Sometimes, under the law of some states. Often there are still formal requirements that must be met. This can be called a holographic will, although, there are sometimes different provisions (see the Michigan statute quoted above, for example).
How can you tell which jurisdiction’s laws apply to your will before you die?
The Will will probably be probated in the state of your domicile or a state in which you have property. If you keep all of your assets in one state, you’ve pretty much determined which states courts will probate the will, and therefore, which state’s choice of law rules apply.
As a general rule, courts will find a will valid if it is valid under the laws of the state in which the testator was domiciled, many (I don’t have a survey handy) will find the will valid if it is valid under the forum states law or the law of the state where it was executed. There are probably some additional exceptions.
So, if you live in a state in which holographic wills are valid, and you are in an airplane that’s about to crash, you’ve got a pretty good chance that your unwitnessed will get be enforced. If your state doesn’t, you’ve either got some quick legal research to do, or you’re gonna have to roll the dice. And if you’ve got multiple real estate holdings in multiple states. . . well . . . cross your fingers.
Getting back to our tractor fender will, I’ve pulled out the relevant Saskatchewan law that would have governed the situation if the farmer had died without a will in 1948:
So if the farmer had died without a will, leaving a widow and children, the estate would have been split between them.
If he had underage children, one reason for leaving it all to his wife might just have been a general feeling of “make sure the wife gets the farm, and she’ll look after the kids.”
I doubt that there would be much detailed estate planning going on in the mind of someone pinned under a tractor.
Whichever one you choose, I’ll argue it should have been another one. . . when we get there, I’ll claim it should have been the first one. Rinse. Repeat. Renvoir. . . dépeçage.