There is a good chance you will be disqualified.
If you fail to answer the summons the case will be heard in your absence. You will not be able to enter a plea (and so qualify for a discount on your fine should you decide to plead guilty). You will not, obviously be given the opportunity to provide the magistrates with any explanation for your excess speed. Nor, more importantly, will you be given the opportunity to explain what effect a driving ban will have upon you. The magistrates will hear just the basic facts (i.e. you were caught doing 67mph in a 40mph zone). They will not ask for, or be told, anything about the state of the road, how heavy the traffic was, or any other factor which may mitigate your offence.
In most areas if the court is considering disqualification they will still convict you in your absence but will adjourn the case for sentencing. They will write to you explaining that you face disqualification and give you one final opportunity to attend. If you do not, then sentencing will go ahead on the new date and you can be disqualified in your absence. (Do not rely upon this second chance. Some benches have a policy of disqualifying in absence without warning).
You can plead guilty by letter (and so qualify for a discounted fine). Your letter will be read to the court but you cannot guarantee that everything you want them to hear will be heard. My advice is to put your best suit on, attend, be humbly remorseful for your sins and hope for the best. Oh, and make sure you take your driving licence (including the paper part) and some method of payment to settle the fine and costs.