I can't speak for Astra, but I worked for and held stock in a company that went private, and the way it worked was you were given a choice to either sell at the

I can't speak for Astra, but I worked for and held stock in a company that went private, and the way it worked was you were given a choice to either sell at the price proposed by the private party that was going to be the new owner, or you retained your shares but they would no longer be publicly tradeable. If you did nothing, the default was, yes, the shares would just disappear and be replaced in your account by cash. If you opted to retain, however, possibly because you were legally required to for some reason, have at it. You just own a thing you can't sell now. If the company ever goes public again in the future, then you can sell.