Abandoning old applications is often not done to avoid frustration by traditional users. By keeping old stuff alive extra complexity is added to the system, piling up clean-up efforts for later. Sooner or later however too many versions of too many systems remain alive and tend to block significant upgrades. This behaviour of not decommissioning older functionalities functions as a time bomb. Some day a clean-up is needed.
Facilitating the acceptance of decommissioning calls for a gentle change management and good information sharing on new functionalities. This change management needs to be tackled properly and entails an inventory of the use of the system, the kind of use (do they use full functionality or do they only use it to export data), the projected replacement of functionalities and the kind of resistance to change expected. This then typically lead towards appropriate communication and training, in order to massage the impact of all changes.
This assignment is mostly part of regular coaching and stretches over multiple months of elapsed time.