The plan begins after a solid winter of base training efforts, time trials and bricks.
Monday is a rest day but obviously adapt these to your own training schedule. And if you miss a session, then don’t panic.
If people miss a session my approach is that you cannot get that time back and so do not go searching for opportunities to claw it back.
If someone is ill or injured and they miss a few days or a week of training then I ask my athletes to simply pick up back in the plan where they should be. I have seen a lot of cases where athletes attempt to include additional sessions into their plan when they have recovered to make up for lost time and the risk of actually getting ill again or injured is far greater. The athlete needs to appreciate that missed sessions are exactly that and move on. This is a difficult thing to come to terms with when their motivation is so great.