Q.I planted a cherry tree about 4 years ago. Very healthy and amazing fruit until this year. Not leaves at all, but tree is alive. I
s this normal? Live in zone 6.

If there are "no leaves at all" what makes you think the tree is alive?
Reasons for defoliation and die-back can be water related, too much or too little, or a pest or disease issue, or an abiotic disorder.
In order to help you with diagnosis and treatment recommendations, we would need a photo and more information on growing conditions, your soil and water management program and pest control. What signs did you notice and when? Did it flower and leaf out in spring and then lose the leaves? Or did it not flower and leaf out at all this year? What changed this year? Was there any soil disturbance, construction, trenching, soil compaction, herbicide use in the vicinity, gas pipe leak, water deficit?