There's is only one thing outside the bot's control, that is Mt. Gox doesn't accept the orders.
In that case, the buy! call will fail the the program will be queued to retry. Nothing is changed in the database.
There are only one variable, which is the surplus. The rest are constants set by the operator.
The operator can fuck up. Settings can be misconfigured or inconsistent. The ticker can deliver poisoned values and so on...
The dangerous cases are when things don't blow up outright, but just go astray.