If some mercenary tried to kill me, I'd probably do the same thing that Ryan did if I could. Depending on who hired me and why they wanted me to kill Ryan, I could have deserved to get my ass handed to me. In that case, I wouldn't blame Ryan for what he did.
But on the other hand, if Ryan is some terrorist or dangerous criminal or something along those lines, yeah, I'd kill him regardless of whether or not I'm still getting paid. Of course I'd learn from Ryan's mistake and go for something quick and efficient, and check to make sure that he's actually dead.
On second thought, I'd probably be really pissed off at him, so I'd shoot out his legs and arms, then use him as a punching bag/trampoline. And then throw him off a building. And then jump off said building and land fist-first on his face.