//If he was banned for 30 months, there is a fair chance that he would have been required to take an extended driving test in order to get his licence back.//
That's extremely unlikely.
The court has the power to order a re-test following any disqualification This will be a normal test in the event of a discretionary disqualification or an extended test in the case of a mandatory disqualification. However, it is rarely used in the case of Excess Alcohol. What is of relevance is, to have a ban of 30 months imposed, unless there are other aggravating features, the defendant must normally have provided a reading of more than 120μg of alcohol in breath (or the equivalent level in blood or urine) where the limit is 35μg . This would place him into the "high risk offender" category. A defendant is High Risk if:
a. a disqualification was imposed for driving, or being in charge of, a vehicle with excess alcohol and the reading was equal to, or more than, 87.5μg in breath, (or the equivalent in blood or urine)
b. there are two disqualifications within 10 years for driving a vehicle with excess alcohol or being unfit to drive;
c. a disqualification was imposed for failing to provide a specimen for analysis;
d. a disqualification was imposed for refusing to allow analysis of a blood sample taken due to incapacity
Before he is allowed to resume driving such a defendant will need to satisfy the DVLA doctors that they are medically fit to drive again. A defendant will have to complete, and pay for, a medical assessment including blood tests before their licence is returned.
So the OP's husband will almost certainly fall into that category. The only way she can find out if a re-test was ordered is to contact the court where he was convicted.
She should do so only if she is interested because quite honestly there is zero chance of any charges resulting from this. Apart from anything else the time limitations make such a prosecution impossible. If he has no valid licence now (because he did not take and pass a re-test if it was ordered) the offence would be "Driving otherwise in accordance with a licence". This offence is usually dealt with by a fixed penalty of £100 and three penalty points.