Aleem,
Isn't it a step by step approach to remove any material from planning. If we say we are removing one material I hope it has a reason but just not like that. It needs to have a business reason example end of life cycle or some other business reason. Which means logically my forecast basically demand should be the first which should not be there. If that would not be there it will not get considered in planing for generating new supplies (planned orders/ purchase orders). Thereafter you need to close all WIP orders and finally decide what needs to be done with existing stocks. Though for WIP & stock part when once dis-continued along with removal of forecast you can do CCR which would show without IM and can be removed in APO. Thereafter business needs to decide finally how to handle WIP & stock. But for APO its more or less clean.
I don't think there is any logical trigger (automatic) which is available. But on the other hand you can create your own. Example you can have plant specific status as an attribute for your CVCs which are considered while releasing your forecast. IF its P (production) this forecast would be released, on the other hand if it changes to A (archive), which means change in CVC (could be automatic also) this forecast would not be released.
Thereafter you can plan a transaction data deletion job with selection profile (through enhancement) for such materials.
It's matter of exploring such options and defining right way of working when once life of material comes to an end coz of any reason.
Regards
Rahul