How to modify TL431 current limiter to work with 80V bus?
how to modify this circuit to work with 80V at input(Vi bat).

The TL431 won't see anything like 80 volts between any of its terminals. The maximum voltage between cathode and reference pin is limited to around 1 volt maximum (BJT \$V_{BE}\$) and, the normal operating voltage between the reference pin and the anode is 2.5 volts. That would make \$R_{CL}\$ in your circuit 500 ohms for a 5 mA current limit.
If you are worried about transients etc. you can use TVS diodes connected across the pins but I can't see you having a problem that would normally need them.
If you need to put your mind at rest I suggest you try simulating the circuit.