First of all - surrendering, or not, is a Ukraine problem. It's not a problem for the United States, but turning it into a problem for us (I presume that is the "we" you refer to, you're not Ukrainian, correct?)
“It’s not a problem for the United States”
If people want to get hysterical about “WWIII”, then obviously they are talking about the United States. Russia nuking Ukraine would not be WWIII by any stretch of the imagination.