What happens to a person who have a stroke...?

and was not discovered until the next day or so... are there any hope / chance of recovery?

ALWAYS hope for a recovery ... Total recovery might not happen
My mother had a major stroke and lived 10 more years! Her last stroke killed her.
If your talking about TIA's (small strokes) you can live even without knowing you had them until it does the damage.
But to find a person the next day asleep and HAD a stroke that will take some hard work on the doctors part to get them back, prayers do help and they work too
I will add my prayers for your person too, Good Luck

In this case where symptoms weren't identified/noticed immediately, there could be two explanations:

It could be a minor stroke, which is difficult to notice and usually resolves itself after a couple of days or so.

However, there is a so called "stroke in evolution" which is a progressive kind of stroke that gets worse over time. It doesn't matter whether it has been found immediately or not for this kind of stroke. The symptoms are bound to get worse.

So depending on the kind of stroke, chances for recovery are relative. However, medical help whether late or not, is greatly helpful for the improvement of the patient's condition.

Hope this helps

It depends on the extend of the stroke. All minor strokes recover fully. Even major strokes recover to a great extend.