Hi there Simrat, 

This is a little tricky to answer without knowing the project particulars, however, generally the following are key to know:

1. Once demerged, is one of the applications being decommissions (in other words got rid of)?

2. Once demerged, are either of the applications changing their functionality (either with each other or with other applications)?

3. Not sure if you will be involved in this or not, but are either being hosted differently (either location or by a particular team)?

4. Will the way a User interacts with them change (the answer to this is 'Yes'). E.g. will they need new log-ins, will the available functionality change, processes change etc?

5. License changes? (again may not be you doing this).

6. Does either of the Applications touch external customers? If either do (either when coupled together or demerged) then a new Customer Journey will have to be thought through. 

7. General communication to those Users effected needs to be thought of. 

8. As a follow on for Point 2 - are other applications effected by the demerge? 

My first tip would be to do a 'As-Is' and a 'To-Be' based on what the applications do, firstly when merged and then when demerged. 

Failing that, speak to the Project Manager, who should have an idea of the above, albeit not in detail.