From a medical perspective, it matters a great deal what the specifics of the diagnosis and treatment were. If the original presentation was straightforward, and the treatment regimen was standard without significant complications, and the patient is in remission, then it would not be unreasonably difficult for a new heme/onc to pick up the case. Patients transfer between institutions frequently. However, for unusual cases, non-standard regimens, or a complicated clinical course, the difficulty of becoming familiar with the prior details would be far greater.
It would also make a big difference what the expected duration of remission is, again based on the details of the diagnosis and clinical data. I understand you don't want to give those details, but there are indeed certain subtypes of acute leukemia that would be less likely to recur including in the short term. It seems based on what you say that this is the case with your husband. If so, that would also make me more comfortable with switching.
*However* ... other questions you should consider: Do you truly trust your current physician? What about your experiences with the affiliated hospital or cancer center? As you may have guessed, I have some experience with the field, and there are certain doctors and institutions I would insist upon seeing in your scenario -- and some I would avoid. If you have already found one of the former, then that is worth its weight in gold.
