An adjective to describe a person who has come back from failure
Solution 1:
"Resilient" seems to be a perfect fit.
- able to become strong, healthy, or successful again after something bad happens
- able to return to an original shape after being pulled, stretched, pressed, bent, etc.
merriam-webster.com: resilient
Solution 2:
Perhaps resurgent
rising again, as to new life, vigour, etc.
Collins
The term is especially apt where there was a lull or quieting of activity before the renewed effort.