I would think that is it hasn't leafed out by July, it is dead or nearly so. You could add fertilizer buy clearly this shrub is struggling and may never return to full vigor. I would dig it up and see if there is an obvious problem with the roots. Look for crown gall as this can destroy a plant. It also indicates that you should not plant another Euonymus species in that spot. Here is info on crown gall. Search for more images on the web. https://extension.psu.edu/euonymus-diseases
Each spring, feed the burning bush just after the plant begins to put on new growth. Use about 1/2 cup of tree and shrub fertilizer per bush. Sprinkle the fertilizer on the ground over the root area of the bush. Rake the granules into the top 1-inch of soil and water thoroughly to start the fertilizer traveling down to the roots.
Locate the burning bush in well-draining soil, because it does not like soil that stays wet for long periods.
Mulching benefits the burning bush by keeping the roots cool and conserving water.
Insect pests can slow the growth of the burning bush. Check monthly for spider mite infestations.
Check the branches; do they bend or snap off and break.
Do this throughout the bush and see what may still be alive.