I think all he needs to do right now is ride a good TT, don't lose time until Bormio and just go all out from the bottom of Umbrailpass which is extremely similar to Blockhaus stats wise (13,4 km @ 8,4% vs 13,2 km @ 8,6% for Umbrailpass) which is coming after a much harder stage this time and basically in 1000 metres higher altitude. I doubt we will see much happening on Oropa, but he did say that Italy was looking for the next Pantani and here he was, so maybe he also wants to win on Oropa. Doesn't take a whole lot from Movistar to control the break on that day since its basically ban plat 120 km leading up to the climb.
Then he can reassess and if Dumo still is in the jersey or if he only leads with 1 minute and under, obviously needs to go very hard on at least one of the remaining 3 mountain stages on stage 18, 19 and 20. Piancavallo being the most obvious, but Dumoulin have decent chances of cracking a bit on stage 18 if raced hard as he have on double Stelvio.