Hello Keerthan,
The scenario is explained very well in the below SAP Help document, please go through it it answers your queries,
Planning with Final Assembly (40) - Demand Management (PP-MP-DEM) - SAP Library
For 1st instance:
The remaining PIR's can remain unconsumed and you can later delete them from the system.Explained in below link,
Sample Scenario: Strategy 40 - Demand Management (PP-MP-DEM) - SAP Library
For 2nd instance:
Read this, Coping w/ Insufficient Coverage of Components - Demand Management (PP-MP-DEM) - SAP Library
Best Regards,
Ameya B.