They had posters up already at Leyland station this morning mentioning this problem, so Northern have been on the case pretty quickly to get the news out.
It will make for a pretty terrible run of non-commuting, especially for those at the further end of the rail replacements (Adlington to Leyland). The buses in to Manchester in the morning have been regularly later than timetabled, even with the quieter traffic, so it won't get much better.
If they could have got a few of the remaining Northern services from Preston to Manchester and vv to stop at Leyland (and possibly even Euxton) than that would help to cover those in the Chorley / Buckshaw area. Northern have said that they requested a Leyland stop, but Network Rail didn't approve them. Network Rail claim no request was made by Northern for this in a response to one of my fellow commuters who acts as a bit of an informal rail user group co-ordinator for Leyland and Buckshaw Parkway.
As already mentioned, it will be a challenge to get the required number of replacement coaches once the schools are back. It will be even harder to stick to the bus replacement timelines when the traffic is back to normal levels too.
Passenger levels will be back up to normal again soon too. The usual downturn in commuters during the school holidays, plus people trying to take time to avoid the closures has helped over the scheduled closure. It won't be fun when back up to full volumes.
Obviously things like this are unavoidable when they happen and it will be a challenge to manage around it. Hopefully NR and Northern can find some solutions to go beyond the bus replacement solution currently in place.