Looking at some aerial pictures (https://pbs.twimg.com/media/D4OFOKMWkAEEHsz.jpg), it looks like the vault is holding except maybe for the section above the transept area (where the spire collapsed), but it has probably suffered, if not from the collapse of the roof, the heat has probably weakened it.
But yes, one or two decades of restoration is a realistic estimation, it's roughly what it took for other cathedrals to be restored (Rouen, Reims) after the World Wars (hopefully Notre-Dame will be in a better state after the disaster)
