Nothing is guaranteed, especially if the format is T20. The advantage for Bangladesh is that two of the teams from each group in the qualifying stage will progress to the main tournament. So they can afford to lose one match. They are in a relatively easy group, along with Papua New Guinea, Scotland and Oman. Of the other three teams, PNG has been in pathetic form recently. Oman do have the home advantage, but their players lack experience. Only Scotland has a chance to make an upset.
Like football, the World Wide Games, cricket has not spread so much yet. Very few countries perform regularly in cricket. The ICC could have increased the number of teams performing in the World Cup if it wanted to. Given the opportunity to play on a platform like the World Cup, maybe the weaker teams would try harder to build themselves stronger, maybe their government would care more about cricket.