Yes he can cancel your visa because he is your sponcer if he does not need you or either you dont want to work anymore for him then according to imigration rules in Qatar he has right to cancel your visa does not matter if you have not done the finger print and medical.
I a know alot of people are not happy with this type of rules and regulation but some in ally GCC countries. your sponcer will simply write to the ministry of interior that he does not need you so he caqn cancel your visa and if you can fing another sponcer and want to comeback i am not quite sure that after how long you can come back