TL;DR: hybrids not only do regenerative braking, they also have an electric boost
Actually, the battery is never full. My understanding is that it is always kept between 40% and 80% of charge to prolong its lifetime. There is probably room for small amounts of regenerative braking when the battery is 80% full. Also, the battery is connected to two (or three in case of AWD) motor-generators. If the battery is close to 80% full, the motor-generators supplement the power of the internal combustion engine. If the battery is so full that the control computer does not want to put more energy to it, the system switches to using disk brakes. You can hear the switch to disk brakes when braking to a full stop. When fully stopped, you hear the brake pads move when the system switches from regenerative braking to disk brake pads.
Some Toyota hybrids have an engine braking position. On my 2016 Toyota RAV4 hybrid, it is actually a manual shifting position which has 6 emulated gears. When you select a lower gear, it means that there is more engine braking and also more acceleration if you need it suddenly. Handy for driving in mountainous regions and joining a freeway. Not so handy for driving down small hills, as this engine braking position does not do regenerative braking.
If you have driven a Toyota hybrid, you have noticed the "EV" light. It means the car can use only electricity to propel it when the power demand is low. For example, on my 2016 Toyota RAV4 hybrid, the battery can provide 42 hp, whereas the total combined output of the hybrid system is 197 hp. So, only 21% of the power can be provided by electricity alone. This means in practice that when you accelerate or drive at high speeds, only part of the energy is provided by electricity and part of the energy is provided by the internal combustion engine.
What is the idea of a hybrid, then? The idea is that gasoline engines work poorly at part load. Let's assume that the optimal energy efficiency of the internal combustion engine is obtained at 70 hp power demand (the electric CVT automatically selects the optimal RPM based on power demand). If you demand 50 hp, it cannot be provided by the battery (that is capable only below 42 hp). So, the engine is run at 70 hp, and the excess 70 hp - 50 hp = 20 hp goes to the battery (assuming the battery is not full). If you demand 30 hp, it is alternately provided by the battery and alternately the battery is charged at 70 hp - 30 hp = 40 hp. So, by alternately using the internal combustion engine and battery, the internal combustion engine is run at higher efficiency. Also, electric boost on demand allows using more efficient Atkinson cycle engines because the electric boost overcomes their drawbacks.