In every loan agreement it is stated that changes in the economic situation must be reported. However, I do not know if the [Grundbuchänderung] is automatically reported to the bank by the notary. If the bank wanted to, it would probably be able to terminate the loan anyway and let it come to a legal dispute.
Registering someone in the [Grundbuch] is a gift and results in a co-ownership share of the house with all disadvantages regarding inheritance (if the parents are listed) or separation (if the new partner is listed).
If the relationship with the ex-husband is good, keep him in the loan agreement and make a separate contract with him stating that you release him from liability or that he receives something from a possible house sale even if he is no longer an owner.
After 8 years, enough should have been paid off so that the financing is secure for the remaining 12 years.