It's not uncommon that someone may initially be paralyzed or not be able to speak at all, and within hours to a week, will improve dramatically. When that happens, we assume that many of the nerve cells initially injured were able to recover, so people spontaneously get better. We don't know of any ability of nerve cells to recover weeks, months, or years later after being damaged. And once a cell is on its pathway to dying, we don't yet know how to help revive that cell. There's quite a bit of research going on to try to reverse the cascade toward death that is initiated by a lack of blood flow, oxygen, or sugars getting to the brain.
Memory loss is very common after stroke.
What determines that is what part of the brain is affected by the stroke, and whether there have been prior strokes or brain injury, or even an underlying disease that wasn't obvious to that point. Many people will improve in the first couple of months after stroke, but some continue to have significant difficulties in learning new information, or retaining recent information. They usually have a lesser degree of disability. There's usually a continuum for rehabilitation in the place where you get it. The most common problems that arise that require some rehabilitation are what we call functional disabilities, or difficulties in doing your own self-care such as bathing, grooming, toileting, eating, feeding yourself, walking, getting up stairs, and generally doing the basic functions we're all used to doing to get through the day.