My husband just had a mini-stroke after having early vascular dementia for 18 months. What can I expect?

He will likely continue to decline. Keep trying to fill in holes in his memory if he doesn't get upset when you do so. If he gets upset, you may just have to distract him from the issue without making a big deal out of it. Sometimes we have to "agree" just to get them to move on. His deceased wife is part of each day because that's where his memory is stronger - longer term memory. It's hard for you, I'm sure, but it's just the disease, not him. Please try to remember it has nothing to do with your marriage. He just remembers the past better than the present.
Keep in contact with the doctor. It sounds like he's getting good care. You may eventually need to place him in a memory unit for his own safety. Good luck,
Carol