At this point Cruz can either join Trump (assuming Trump invites him) or get left in the dust.
If it’s option #2 then he can go quietly, or he can do his best to help the liberal uniparty establishment get President Hillary elected like the rest of the neocons are bent on doing.
Or he can finish out the primaries, see how the cards are dealt, and then he and Trump can decide what they're going to do come convention time.