NELI is best delivered by the same member of staff to ensure a consistent approach to the intervention. If the staff providing the programme to pupils is absent for a prolonged time, consider pausing the intervention and negotiating extra time to extend the intervention. When you restart, revise the sessions of the topic already covered and then move forward to the new sessions for that topic.
If the likely absence length means the 20-week programme no longer fits into this academic year you can instead request for another member of staff to access the online training so they can deliver the programme to pupils in their place. Splitting the delivery of the intervention between staff is much better than not being able to deliver the intervention at all.