Rubio *has* made and *is* making a choice right now between Cruz and Trump. If he prefers Trump, he stays in. If he prefers Cruz, he gets out. It won't be Rubio in either case.
I hate to tell you this, but you're exactly right, and taken as a whole, a dream scenario for Trump.
If Rubio wins VA, and Cruz wins TX? Trump makes the convention with about 200 extra delegates to win first ballot...