Delisting a company from exchange

What are the implications of delisting a company from exchange? What are the risks associated?

There are few foreign companies that have their clones in India like AstraZeneca, ABB, Honeywell Automation, etc… when these companies delisted (could be of any reason, merging with other, exiting from India, etc… (I don’t mean the situation of bankruptcy)), how can retail traders encash their shares?

Looking for more information on the subject from experts.

P.S.: The company names are for example only. There are about 29 such companies.