No problem. I'm again going to refer to an old online game Netrek. The way it worked is that players could join and leave at any time. When they first joined, the were placed in a wait queue. If there were other players and bots in the game, it would wait for a bot to get killed (or kill a bot if no players were near it) and then replace that bot with a player. If there were no players in the game, it would kill off a bot and load the player.
Just something to think about. But without promoting your game, you'll just have bots running around.