It should be possible with an AMX plugin. I've written such a plugin for realbot, joebot and yapb. If you're interested I could port it to HPB bot too...
"Is it possible to auto kick the BOT if the 'real' player count in my server is 2 or more and then add him back if the 'real' player count is 1 or 0??"
That's what the "min_bots" and "max_bots" values are for in the HPB_bot .cfg file...
min_bots 0
max_bots 2
...this will add 2 bots when the player count is 0, kick 1 bot when the player count goes to 1, then kick another bot when the player count goes to 2 or more.