What was the grocery store she walked too and never came back? Is it still there, or fallen too gentrification, economic loss , bankruptcy, owners retire.....?

The store was named Thomas’ Country Store. I am unable to find a source that gives its exact location, but Kari lived at 26 Palmer st and the timeline of her whereabouts say that she left the store at 9:55 pm and was last seen at about 10:05 pm and was 700 feet from her home at that time. Based on that I would suspect that wherever it was it was a location within a 10-15 minutes walk from her house. Looking at Google Maps, this store (now a family dollar) https://maps.app.goo.gl/BxjKDA1oCPb8p4Vo7 is an 11 minute walk from her home address. So my educated guess would be that it could have been at this location, but I can’t say for certain. I did read that the owner of that store passed away in 2019 at the age of 72. So my guess is the original business has been closed for quite sometime.

This took some digging to figure out using what I could find online, but this is my best guess.

The wiki and other sources give the name of the store as Thomas Country Store, in Au Sable Forks.
Other sources also give Nixon's home as being on Palmer Street.

Looking for Thomas Country Store however, pulls up no current business. There is an obituary for Thomas M. Thomas (yes really) however which indicates he was the owner. He died in 2019. The business registration for NY state is still active, which means nothing, but it was originally filed in 1986.

Interestingly, the address given for the store is 10 Railroad St Ausable Forks. The problem is no such street exits in that town on any current map.

I assumed the street was renamed at some point. Searching for it brought up little, but I did find a photo from the 20's showing Railroad street and a sign pointing to Plattsburg. Although I had a hunch which intersection that photo was taken in, the buildings had changed too much by 2009 to make a positive ID.

My guess had been that railroad street ran with a railroad line, which helped to rule out most roads due to topography issues. Further investigation of the town history showed that this was correct, and a railroad line ran in the street at one time.

Finally I found another image which positively identified the intersection as the present day intersection of Route 9 and Main Street. That photo contained a distinctive building, the American House, which appears in the photo I mentioned previously. This confirmed that railroad street was in fact the present day Route 9, called Ausable street.

However we still have a problem because the addresses are not numbered from the same location, so there is nothing close to 10 on that road. However, going off the assumption that 10 had to be close to the intersection of Main Street and what was at the time Railroad Street, which is bolstered by the address numbering on Main street, I narrowed the range of buildings to a handful near the intersection which show up in historical imagery for the 90's and are commercial in character.

That still only narrowed it down to a few, including what was a Deli in the mid-2000's before becoming a pizza place and a present day Art and Antiques location. However, what finally narrowed it to what I reasonably believe was the right store was finding a different record for Thomas’ Country Store which delt with…an environmental incident…specifically a gasoline spill. Thomas’ Country Store was a gas station. The store being a gas station makes sense given that it was open at the relatively late hour Nixon went to it.

Thus, I think the present day address of the store was 2499 State Hwy 9N, Au Sable Forks, NY 12912. In historical imagery this shows as a gas station, with a grocery and deli. The sign in 2009 says "Only at Rod's" which leads me to conclude that by that time the store had changed hands and names, reasonable since Thomas M. Thomas would have been 63.

Based on the historical imagery, I can say that the store had rustbelted by 2014, and was for sale. Some point between 2017 and 2019 it was demolished and a credit union built in the place.

https://www.google.com/maps/place/Peru+Federal+Credit+Union/@44.4415325,-73.6747375,3a,75y,160.76h,87.46t/data=!3m8!1e1!3m6!1sD34UXDY4qTQFMVyi4y4wpw!2e0!5s20140901T000000!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D2.5421961314118846%26panoid%3DD34UXDY4qTQFMVyi4y4wpw%26yaw%3D160.76147909804484!7i13312!8i6656!4m6!3m5!1s0x4cca584009e62623:0xbf2096bc06dc47f9!8m2!3d44.4412759!4d-73.674677!16s%2Fg%2F11hy9p3299?entry=ttu&g_ep=EgoyMDI2MDIwMy4wIKXMDSoASAFQAw%3D%3D