1. In order to be found guilty of drink-driving the police have to show that the driver was over the limit at time of driving. This clearly does not apply here, so your question is a little odd.
2. You can report to the police that he drove while disqualified from driving. They may take action though, given the timeline, think it most unlikely.
A quick phone call to the police should give you the appropriate advice.
3. One wonders why you want to pursue this. A better course of action might be to get on with your life though, if there are contingent issues like child custody, I can see why you might want to take matters further.
4. If you mean 'is there a statute of limitations on breaching a ban order' then there is, but it depends on the punishment given at time of ban.
Hope that is moderately helpful.