What might be causing an op amp to fail in a voltage follower circuit?
I suspect this Op Amp has no business being in this design.

It has near rail to rail output using a push=drain&lt;>pull=collector rail to rail driver when you need a Darlington complementary Emitter-Follower for stability.  If/ when it oscillates from certain loads not specified in the datasheet such as yours, it may suffer from oscillation and shoot-thru failure on the low side as it has an NTC tempco BJT collector output which rise in current gain and BW with temp, making it a good candidate for unity gain oscillation.

Upon reading the Phase margin plots for this it is clear the phase margin drops to zero with rising capacitive load and even though you have 200 Ohms in series, I expect this IC was running hot with > 1/4 W and burnt out in a matter of minutes with thermal runaway on the low side as current gain and current limit rises with temp thus raising the oscillation power consumption.



Solution use any buffered BJT Op Amp, not a Rail-Rail FET type with a BJT low side drive. You do not need RRIO type OA. If you want more current drive, add a push-pull emitter-follower inside the unity gain loop.



This shows Phase margin reducing with rising capacitive load, a feature not found normally found in unity gain stable BJT Op Amps with active current limiting.