Hi Praveen,
Make association between both entity 1 to 1 or according to your requirements.
When you go to second page -> Take first entity parameter in this page -> take a dataview -> take dataSource as microflow in this microflow->
Retrieve your second entity object by association of first entity object then take a decision and check object is empty or not $SecondObject!=empty.
If condition is true then return your retrieve object if condition is false then create a new object of second entity pass association inside this object & commit the object ->then return newly created object.
Hope you like the answer.
As per above conversation, Then 2 object should be associated with 1 to 1 association. For Eg: Object1 and Object2
In the First page maintain a dataview with Object1 and pass the object1 to second page by make dataview of Object1 and Nested dataview with Object 2 with Association. Therefore your data won't vanish