Even if Sam tells everyone that Tyler won the Cloud App, I doubt it would matter. All he has to say is, "Yeah, I won it. But I didn't use it. I didn't let it affect the game." I don't think anyone would argue with that. Heck, Hayleigh revealed herself as the hacker and still stayed safe for weeks afterward.
I really think Kaycee's best bet would be to take out Tyler this week. Since Angela can't play HOH, Kaycee would most certainly beat JC and Sam. Even if she doesn't, she can easily sway them to set their sights on Angela. Then Kaycee would be final 3 with Sam and JC. Something really odd would have to happen for her not to win the whole game against them.
I don't think she'll do it, though. What always gets me about BB is that it's an individual game. There's only one winner, but people have to work together to make it farther in the game. In the end, some players choose to stay loyal to allies rather than go all out for themselves. The stronger personalities guilt the weaker ones into sacrificing themselves. It will be interesting to see how the final weeks play out.