How does this BJT affect the circuit? If it does, how should I simulate on Circuitlab to see the effect?
You are right the Q23 will be ON. Why? 
Because there is a path for a base-collector current to flow for NPN transistor to ground. 







simulate this circuit &ndash; Schematic created using CircuitLab

And in this reverse connector the collector took over the role of the emitter and the emitter now takes the role of the collector. 
But due to the different doping (and size) between the collector and the emitter. The reverse beta \$\beta_R\$ will be much lower than the "normal" forward beta \$\beta_F\$.

For example my BC548B show this resoult: 
\$\beta_F = 250\$ at \$1\textrm{mA}\$ and \$\beta_R = 8.3\$ in reverse active mode for the same current.    

And for BC337-25 \$\beta_F = 352\$ ; \$\beta_R = 38\$  

As a side note the BJT will also conduct current in these two cases:

BJT as a Zener diode



BJT's now behaviors just like a poor's man tunnel diode (Esaki effect).
And tunnel diodes will have "negative resistor" region.
And this negative resistance region occurs only for NPN BJT's.


http://jlnlabs.online.fr/cnr/negosc.htm

http://www.cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html

BC337-40

Veb=8.2V , Vec=6.7V at I=5.5mA

BC549B

Veb=8.3V , Vec=7.2V at I=5.5mA

BD139-16

Veb=8.5V, Vec=6.7V at I=5.5mA