It's not a stalemate.
You have a number of options in this scenario. First, you can just pop your NV, buy 4 provinces and 2 duchies, best they can do is match you. Or if you're second player, not even that. Other options including buying money, and then shifting that into your mat every turn. The only issue you might have is getting down to 1 NV in deck, then having the possibility of missing that NV as your 6th card, thus not being in your hand. On the other hand, if you have some particular reason for doing this instead of popping NV, this probably isn't going to be a big deal.
Depending on what's on the board, you can slam down some more engine components - particularly any other source of +buy is critical. Just make sure that your opponent can't end it on you - keep track of how many buys they can slam down at any moment, how much money they have, etc.