Didn't Coleen Nolan stand in for her or Christine on DoI?
The revised format though can clearly cope with one presenter.
Coleen stepped in for Holly one week when she was taken ill.
Philip did actually put on his instagram before the series started that they have contingency plans and scripts should someone be taken ill during the course of the show where Philip or Holly would just present solo. I would imagine Philip will be on his own or maybe Christine could step in now she's just back from maternity.
January 9th 1989 - December 3rd 2006