Are BJTs used in modern integrated circuits to the same extent as MOSFETs?
No, BJT has less extent than MOSFET because BJT is used where we need more speed. 
But MOSFET is used where we want less power dissipation, low operating voltage, less noise, simple manufacturing process, low chip area and easily scalable.
Now, we use both devices as BiCMOS (BJT + CMOS) which has more speed than MOSFET and low power dissipation than BJT.
Another main application of BJT is oscillators. BJT is better than MOSFET as oscillators.