what do you make of Doc Scratch saying the alpha timeline won't allow for John, Terezi, or Karkat dying?

I feel the implication was, rather, that Karkat, Terezi and John still had a purpose in the Alpha Timeline. John, specially, is an extremely important part of the Alpha Timeline to gain the Retcon Powers and bring Lord English into being. Karkat and Terezi have less defined roles than that, but they’re a big part of the group through Act 6, both in the GO! Timeline and in the Retconned one. Not sure to what extent Scratch knew about this or how far ahead Hussie had planned. Perhaps he knew already about Vriska being brought back by Terezi’s planning? Hmmm.