Or meet up with said colleagues at an industry event, because the world is awkwardly small. So it's in your best interest to make sure that your resignation letter is clear, concise, and polite. Here are some best practices you can follow to make your big exit a professional one.
Otherwise, look to the history of your company. How have your boss and other managers handled employees' resignations? If you see a pattern of upper management refusing to let the team members work out their notice, you can likely expect the same.