Are we meant to sell everything...?
Are the shares being transferred to another exchange..? Which should have happen before the 'CLOSING' announcement.
If transferred to another exchange, which one...?
That is up to the issuer of each asset. Contact whoever runs the company you've invested in for details.
Needless to say, some issuers will handle this transition more fairly than others.
Every share holder contacting the issuer is not going to help the process or speed things up, it is probably best to give them a few days(the ones you trust anyway) to sort alternatives and figure things out for themselves as i doubt BS gave them anymore notice than the shareholders.