Hi Tom. I don't think we've had a sale of a company yet, but we have had delistings due to companies going under as in 1time or African Bank.
In the challenge we normally don't do anything in this case. The value of the stock just doesn't update anymore. You could sell it and put the money somewhere else, but there won't be any automatic option.
I'm not sure what a real brokerage does, but I'm sure someone will post something.