AI already move around when a player sneaks. After a certain amount of damage, AI begins to run around, or kite since they can't see what's hitting them.
Moreover, sometimes the AI takes a sharp turn. This often occurs during the player turn, so the unstealthed player can just move out of the cone of view.
I can see serious problems with AI looking around as soon as the player has sneaked. First, how far do they look? What is the range? It can happen that stealthed player just stay out of this range and use a bow, essentially needing to work even less than now to pop enemies.
Stealthing in RPGs is always problematic, and really almost always broken. This is because most development studios do not spend time developing proper AI, they would rather concentrate on things that matter more to the players (i.e. gameplay, graphics, animations and the world).
For an interesting approach to AI programming in games (which will probably be implemented in 50 years if we are lucky) I would suggest looking at
https://www.youtube.com/watch?v=dD9HGw1ZTZY and
https://www.youtube.com/watch?v=6e_xC0MxmvE.
