You might see miniscule change in shape due to stringing and especially stringing with high tension or big cross and main string tension differences. But, most modern graphite rackets don't have a real significant issue with warping.
I use to have a friend decades ago who played with the Red Head which was aluminum with a red plastic throat piece. His red head warped a lot because he would throw it when he was frustrated and it would bend the aluminum. He would correct the problem by banging it on the court to bang it back into shape which was a funny site. He would stare at his racket to determine where he needed to whack it and then flip it around in his hand to get the right angle before he whacked it on the hard court. Repeat until he had close to the original shape restored and then play on.
I have three Red Heads and they are all fine. I haven't used one in many years though. Aluminum frames are good if you want to pound the ground with them as you can keep playing with them afterwards (not talking about the OS aluminum frames). You really can't do that with graphite racquets.
No worries about an unstrung, modern racquet becoming warped.
I know that a few of my woodies are susceptible to this due to high humidity and/or extreme temps so I'm careful with them. Some of my nicer acoustic guitars are kept in a temp/moisture controlled area because of warping and cracking; now they have to be kept strung or the neck will warp (unless the truss rod is adjusted).
With modern racquets I would imagine that warping would be caused by faulty production, poor string jobs (e.g. improper balancing, bad clamping), accidents, abuse, etc., but not being left unstrung.
I've found a number of racquets that have been discarded, left outside in the elements for days. One of my favorites, and one that I still play with, is the Dunlop MW 200G - I cleaned it off, strung it up, and played with it. Racquets made with modern materials can be pretty sturdy!