Before taking a person's license, DPS grants a smidgen of due process to the license-holder, but you must move quick.
Your son has 15 days from the presumed receipt of the letter (which is 5 days after the mailing date) to request a hearing. If your son does not request this hearing within the 15 days, then there is little he can do to fight the suspension. If this is the case, he may still qualify for an "essential needs" license, also known as an occupational license. However, the occupational license will severely restrict the times and locations to which he may drive.
In short, your son needs to contact an attorney now to ensure that DPS receives a timely request for a hearing so that he can fight to keep his license.
This answer is based upon the limited information provided in your question, and is not intended to be legal advice nor create an attorney-client relationship. For more information on your particular situation, please contact a local attorney.