Can an untreated deep pocket tooth turned to cracked tooth? And is the 3-D scan the only way to find out if it's cracked or not?

The deep pocketing your dentist recommended was more for a periodontal problem. If there is a crack anywhere (tooth or periodontium), laser won't do much to fix it. The scanning may help identify whether there is a crack somewhere. If so, depending on type of crack and location, the tooth's prognosis isn't great. If there isn't a crack anywhere, that's great news! He or she would just need to treat your periodontal problem.I hope that was helpful

There are many possible causes of a deep pocket.  It can be gum disease in which case cleaning the site out and decontaminating it whether it be with a laser or conventional tools, should resolve the infection and make the site stable.  If the tooth is fractured, the aforementioned will only gain you a little time before the bleeding, swelling and further bone loss returns.  Fractured front teeth tend to be associated more with teeth that have had a lot of work done ie have had crowns, root canal treatment or alternatively they have received trauma.  These factors will help discern the cause of the pocket.  A 3D dental image can often reveal the presence of a fracture but not all the time.  It is probably wise to get as accurate a diagnosis a possible before committing to any treatment.