I have friends who had morning sickness all throughout their pregnancy. There are also those who had no morning sickness at all.

When I was pregnant, I had morning sickness for about the first three months or so (first trimester) and I think this is generally the usual length of morning sickness. After three months, you'll either got used to it, or have some kind of routine that makes it less likely for your wife to vomit (like, identifying what kind of food, smell etc that made her sick or drowsy). The gas, constipation, heart burn, back aches etc are usual companions as well...

So, good luck and enjoy the ride!