Q.Fungi on Indian Hawthorne
If I cut off all the infected parts of the plant there will only be the bare base of the plant (no foliage), will the plant grow back?

Certified GKH Gardening Expert
Although Indian hawthorn can survive severe pruning, I do not recommend cutting the entire plant to the ground. You can replace the plant entirely, or you may wish to cut the plant back to 6 or 8 inches, wait for new growth to appear, and then eventually remove the rest of the diseased branches.
Here are a couple of articles you might find helpful:
https://www.gardeningknowhow.com/ornamental/shrubs/indian-hawthorn/indian-hawthorn-pruning.htm
https://www.gardeningknowhow.com/plant-problems/disease/plant-leaf-spots.htm