A Terrible Idea. Many grocery stores share a common building or mini mall and the additional sales in the grocery would be offset by the loss at the liquor stores.
Who would police the young people buying liquor most of which are under 21 but who have Id's which state otherwise. The check out clerk is also usually underage as well and may be a friend or classmate
If the long term plan is to close the liquor stores
how would the grocery stores be able to make room for a decent selection of Brands and Prices. I believe it takes about 6000 square feet not including storage to supply and stock a decent State liquor store. Where would existing Grocery stores find the room for a decent display. Only the large chain stores have that ability.