Bruning could not have lasted until 1934; the reasons that he resigned in 1932 will still arise even without the NSDAP. In any case, his policies were nothing like the NSDAP's, and unfortunately they only made the Great Depression in Germany worse. To add to this, Bruning was ambivalent towards the idea of democracy anyway - he naturally leaned towards authoritarianism.
Bruning had very little support from the Reichstag when he first took office, his economic budget was almost immediately rejected by the Reichstag and when an election was called to try and resolve this issue he was left with almost no support at all. After 1930, laws in Germany could not be passed without Hindenburg, which basically rendered the democratically elected Reichstag irrelevant.
The simple fact of the matter is that after 1930 Weimar democracy is finished no matter what you do, and it is almost impossible to revive after this time without some serious constitutional changes.