If you are offside you are offside, that's like saying well the puck only crossed the line by a millimeter so it shouldn't be a goal.
The most crucial call in hockey is whether the puck crossed the goal line. Offside, icing, and penalty calls are not of the same magnitude of importance, even if these calls can change a game. Offsides for me should be made in real time no matter what. Ideally they have an electronic system to do it, but until they have one they need to trust the refs, which we do with many other very important decisions.
Calling back a good goal for a mistake the refs missed 5, 15, or even 30 seconds later is incredibly disappointing and a giant momentum changer. It's not tragic for me if players get away with being an inch offside from time to time, sort of like how the NBA gives some leniency for travelling and the MLB has different strike zones with different umps. It's important to get calls right as much as possible, but to turn back time and reassess a play that happened several plays ago is ridiculous to me.