Hello Akshay,
Fist of all Welcome to the QuickSight Community.
I would recommend first of all to understand what exactly is SPICE and how it works.Importing data into SPICE - Amazon QuickSight
Estimating SPICE -Importing data into SPICE - Amazon QuickSight
Managing SPICE capacity -Managing SPICE memory capacity - Amazon QuickSight
There is no retention period or Expiry of Data set. It remains unless you delete it it.
Hope this helps.
Cheers,
Deep