I have had a Rhubarb plant for three years. However, last fall I planted Garlic seeds close by. This spring the Rhubarb just hasn't appeared at all. Is this a coincidence?
I don't believe the garlic played any role in the loss of your Rhubarb.
Did the plant go to seed? This can rob the rhubarb of nutrients.
Here is a link about Rhubarb.