What will happen if crypto vanishes overnight or due to some or the other reason if crypto becomes inaccessible to public? I know this does not make sense as crypto will not vanish but still what if it happens? What about those huge chunk of investments made by whales and other investors?
No, it makes sense at some point because some countries may ban it, for example India plans to ban bitcoin but I believe they'll change their mind, it's not beneficial in any way.
The reason bitcoin can be vanished is following: It is used for money laundering and illegal activities, so if governments decide to ban it, they'll stick with this reason. But you know what will happen? Bitcoin may vanish but there will be something better and safer than bitcoin for such things and it will be 100x hard for them to detect and vanish so at least in near future they won't make any moves to my mind and so we can say that it doesn't make sense to vanish crypto. Btw it's still good thing to discuss, like when I read others' opinions.
Criminals, at least the smart ones, will not use bitcoin for their crimes since they know they can be tracked, now most of them are using coins like Dash or Monero to hide their activities, and those are the coins the authorities are really watching since they know they are unstoppable, but even if at some point most governments ban cryptocurrencies it is arguable if this will make their price to go down, if anything this could make them even more valuable as it happens with all the good which are made illegal.