The moment you have a ticket the railways must transport you. If not by the originally intended services they will have to provide alternatives. So if you buy a ticket, you can be sure that it will permit you to travel. It is of course possible that because of those engineering works your trip will end up longer.
Railways cannot cancel tickets at their own discretion. So you have a ticket, you can travel.
It is common in Italy that replacement services only get published a few weeks in advance. For travel in November it is not really needed to be so early. If you want to get a Saver Day Pass you should get it, and then just buy Milan - Domodossola separately.