This is a great sign that the NBN won't be scrapped by any upcoming parties.
Unfortunately, this is not the case. What the Government and Telstra have signed is a "Heads of Agreement", which is not a binding contract; it's more like a broad set of terms both sides agree on.
The finer details still need to be discussed and the resulting contract approved by Telstra's shareholders before we can really rest easily. Until then, either side (incl. the next Government, should it change) can pull out.
It's definitely good news – not least for the current Government, coming fortuitously a scant day after a by-election hiding in Sydney –, but some commentators have already suggested Telstra holds a bit more of the bargaining power going forward as a result.