Sorry, but this is simply wrong. Once granted, employment visas are good until their expiry date. You cannot work for anyone else without applying for a transfer of sponsorship, but you are free to live in HK (and come and go as you wish) until the original expiry date of the visa. This is a bit of a lottery because that could be anywhere from no time at all up to 2 or even 3 years, depending on when you are terminated by your employer relative to your visa renewal/expiry date.