Is Jensen right in assuring Strunk that he will not carry out their agreement and kill Strunk? Why or why not?

Yes, they had an agreement, and both men meant it when they initially promised to end the other's life if something happened that would maim or cripple. It's easy to make those agreements but even easier to break that type of promise when faced with it. Strunk was rightfully terrified, Jenson rightfully apprehensive. In the end, Jenson is relieved that Strunk didn't make it.... first, because he would have been a cripple...... second, because he wasn't able to keep his promise.