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This looks like a case of plant edema, an environmental disorder that happens when plants absorb water too quickly. Please see these articles for ways to help your plants recover.

https://www.gardeningknowhow.com/plant-problems/environmental/treating-edema-in-plants.htm
http://ipm.uconn.edu/documents/raw2/Non%20infectious%20plant%20disorder%20Edema%20Oedema/Noninfectiousplantdisorderodema.php?aid=233
http://extension.illinois.edu/focus/index.cfm?problem=drowning-and-edema

Make sure you have not used to large of a pot. In most cases the root ball should fit comfortably with about an inch extra room.
Generally going up one pot size is a good rule of thumb. Use a good commercial potting mix and make sure the pot is draining any extra water.
If you can let us know the type of plant that you have, we can give you more specific care information.
https://www.gardeningknowhow.com/houseplants/hpgen/

It depends upon the plant or shrub you are grafting. For trees and shrubs the grated area can be sealed with a tar like product called Tree Wound Sealer that is available at some hardware stores such as Ace Hardware and some garden centers. It can be messy to work with but does its job well. In other cases once the graft has been made and is temporarily held in place, the entire grafted area can be sprayed with a good fungicide such as Green Cure or Immunox, let dry and then the final graft protection wrap/covering applied. The final wrap area can be sprayed again as well. This early spraying gives the graft a chance to get set and truly take before any fungus can even think about making an attempt at an attack.

This can be a number of things:

It could be lacking light, or being over-watered.

It could be lacking nutrients, and depending on where the yellowing occurs, can be a number of deficiencies. Make sure you fertilize every few months with an all purpose fertilizer.

It could also be a pH issue. use dolomitic lime to adjust pH.

It could also be bacterial or fungal. Use wettable sulfur in the soil to control this.

The best thing to do is to repot your plant in fresh soil without fertilizer and to avoid over-watering the plant while it recovers. Make sure it gets enough light and enough water, but that the soil is allowed to dry out between watering sessions. Hopefully it will recover. Also, if you know the name of the plant you have, you can look up its fertilizer requirements and other care requirements to make sure it stays healthy.

I'm sorry to hear it broke. In the short term, your leaves have no roots to feed them or provide water. As a result they die. Remove most of the leaves to reduce the demand for water. Change the water when it begins to get cloudy. Check out this tutorial (with pictures) on how to root plants in water. http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/visual-guides/rooting-cuttings-in-water.aspx