The day they successfully recreate a t-rex is the day that we start the downhill race of the extermination of our race. Eventually they will be available to the rich individuals who can afford to take care of one. Such at the few on this site who have 1,000 gallons who can take care of monster fish such as red tailed catfish for example. After a while they will be commercially bred on huge farms. Maybe some will get out because a company took short cuts and used cheap crappy weak material. Maybe they will start breeding in the wild. Then we start getting taken out by them. The government will have to get the army involved and good luck killing one. I think a tank would have trouble hurting one.
Nuke the planet to destroy a group of t-rex's that have established themselves into a breeding group and are expanding? Possibly.
But lets not forget about the potential for them to be used by terrorists! I don't know about yall but when I was a child I always dreamed about riding into town on a t-rex and destroying stuff and laughing as they could do nothing to stop me.