I don't think so. Cruz has been pretty rough on Trump for 'ducking' the debate. If he skipped it too it would reflect pretty poorly on him. And paul has finally made it back to the big kid's stage, he's not skipping that!
Cru and Paul cut a deal with McConnell early in 2014 in order to get his and leadership’s approval to run for President in 2016. In return they promised they would not campaign against any incumbent Senators running in 2014. They even gave Cruz a Top spot on the NRSC. Paul and Cruz carried through on their promise by not opposing a single incumbent and kept quiet during the Mississippi fiasco.
They are just an arm of the GOPe now. They sold their soul to the devil.