At least in my city the convention is essentially that a POI node represents a shopfront (though the nodes typically duplicate the address tags). When the shop closes, we mark it as disused. When it reopens, we update the tags.

While it's closed, StreetComplete, Every Door etc. will regularly ask their users if someone new has moved into the vacant unit, so keeping the node around is practically useful, it encourages resurveying.

If the building is demolished or the shop unit converted to residential, we of course delete the node. 

