Will my redbud trees grow new branches up top?

It is very unlikely that the redbuds will resprout in the upper crown. The decline could be due to winter injury/low temperature injury. Newly planted trees are more prone to low temperature injury. Redbud is also sensitive to stem cankers, a disease that the girdle and kill trees. The sprouts from the lower trunk may be trained into a desirable tree but you may consider replanting with a hardier species such as crabapple or hawthorne.