I personally don't like this for a few reasons
- Bot's are really bad
- If you're just disconnecting for a couple of minutes, you don't want to reconnect in the middle of a team fight.
- The bot may buy or sell items you did not want them to.
- It may not know it's role or what it's meant to do (e.g Bots can't jungle yet, as far as I know)
- Bot's are really, really bad.
I think this is a good idea to look in to, and they no doubt have, but the AI just isn't good enough yet. It's also a little bit controversial as not everyone wants a bot to take over for them when they disconnect (I don't).