The best way to resolve the issue with respect to your share of the presumed refund of your security deposit where you cannot get in touch with your former roommate to cash the check that you are writing about is to do as follows:1. contact your former roommate to see if he or she will accept the retirn of the check you have and write two checks (one to you and one to the former roommate) for one half of the amount of the refund explaining that you cannot find your former roomate.Hopefully the former landlord will be understanding and will follow the above suggestion.