I’m not a political consultant but as I understand it, Rubio and Kasich can keep running as long as they want. The problem is that PACs may quit supporting them and people will probably quit contributing to their campaign; therefore, they may not get far without money. In addition, I think most people like to support and vote for a winner so they may not get many votes and a lot of the states going forward are winner take all.
I’ve heard that they’re hoping for a brokered/contested convention and think they can win the nomination there. At this point in time, unless something big happens I don’t see how they can win. All of the foregoing is of course just my HO - think there’s a lot of speculation going on now.