Natural for DB2

We have Adabas and Natural on mainframe.
If Adabas is converted to DB2, and Natural Applications are untouched, instead use Natural for DB2.
What are the pros & cons in going for this approach ?
What changes needs to be made to the Natural Source code (especially in regard to PE and MUs ) ?
What challenges or difficulties should we expect ?
How about performance ?
Are there any other issues we need to consider !!