So I think if we buy Stable coins with some stable volume, we will no longer need to worry about unable to sell our bitcoin into fiat.
Rather we only need to do this thing right? is this some acceptable alternative or no?
That is not bad idea - to invest in stable coin. But this stable coin should be trusted and have a good volume. Such good is like USDT or USDC. That is much trusted coins. Another good stable coins can arrive but need more time.
It is the very same concept that allows you to trade bitcoin against the dollar and if you can sell it and buy it at the right time you can get more bitcoin in return, so I do not really understand why you are so surprised that something like that can be done and sometimes it is even a desirable thing to do.