I'm not sure what you mean by How Risky are HDFC apartments...
Find a neighborhood that you like, and a space that you can enjoy, renovate it, move in, and enjoy it. When you sell it, you will not lose your money.
When purchasing an HDFC Coop, however there are details that vary, so pay attention so you are informed:
(a) Income restrictions vary and are updated every year, as they are percentiles of median income
(b) Seller paid flip tax or building funding fees vary per building, so find out what it is when you wind up selling
(c) When does the HDFC status run out?
(d) When did the HDFC become an HDFC Coop
Best wishes, always