3 issues with this:
1. Wizards are completely screwed. Try to cast something like LoV without accidentally starting fights with wandering real players.
2. Because bots don't play with any real skill, they're always over-leveled for their maps. Can YOU defeat 12 identical level 90 Bowling Bash bots coming for you from all directions at once? I certainly can't.
3. Bots play 24/7 and have no emotions. When they die, all you've done is taken them out of their farming cycle for maybe 3 minutes. When players die, over and over and over again, to bots that now kill them instead of just kill steal them, they give up. Result: The bots OWN the map, they don't just pollute it.
Now... if people want a couple of open PvP maps for the fun of -directly- competing with other people hunting on the map, that actually would be fun (just make sure it's a limited number of maps). As an anti-bot measure, however, it's terrible... you're giving the bots MORE control, not less. They WILL be re-programmed to PK.
Bots will have to be able to recognize each other, in other words they will need a FoF system of sorts. Fail that and hordes of bots will fight each other, accomplish such a system and players will probably be able to abuse it (depends on FoF implementation ofc).