I'm sorry to learn of your father's death. To answer your question, I would ask a few questions of my own.
Did your father ever stop loving you before he died?
If he were alive today, would he continue to love you?
Did your father's love for you help you to achieve your educational ambitions?
Has he love for you helped to shape who you are today?
I already know from your question what the answers will be. I think, therefore, that your father has every right to the dedication you want to make to him. He has loved you, sponsored you, worried about you and encouraged you to this point and the only reason he cannot physically show his love for you now is because, sadly, he is no longer alive.
I don't know how old you are but your Dad put x years of love and work into you - and it is your thesis and your way of recognising what both your mother and your father have contributed to make you the scholar you are today.
As for the rest of the world, it is an unfortunate fact of life that no-one else will actually care about the wording of your dedication. However, your thesis is the culmination of your studies, is something intensely personal to you and - I imagine - you will keep a copy of it for many, many years to come.
If you do dedicate your thesis to your loving parents, no-one but you and your mother will care - but it will mean something important for a long time to come.
If you only dedicate your thesis to your living mother, she will be hurt (assuming she loved your father).
If you do not dedicate your thesis to your father and mother together, no-one else will ever care ... but you will and you will live to regret your decision for many years.
Be proud of who you are. Be proud of how your parents have helped you. Dedicate your thesis to your loving parents and you will have something to treasure.
P.S. And write the very best thesis you possibly can! Good luck.