From past experiences, I'm fearing that lamp filament fusing have negative effects on the ballast, even on 230V mains.
I'm suspecting that the failure of one of the former Opple 24W T5 HO lamp fixtures of my father , shortly after he installed the Osram FQ 24W/840 HO lamp, is strongly related to the lamp filament fusing on the former OEM lamp of the fixture, that probably killed the ballast.
This means, that to ensure long life of my Hyundai 21W T5 normal output fixture in my room of my hostel, I will have to replace the OEM lamp, before it reaches EOL, if it shows massive blackening when its operates, even after it reached full brightness (Which is usually means that the lamp have only few lifespan left), in order to prevent the lamp filament fusing from being executed, and kill the ballast of the fixture, or severally short its lifespan.
Is this true?

As the lamp reaches EOL its voltage begin to rise, so stress the ballast more. This can give the ballast some hard time (when the lamp is blackening but still lighting for its entire length)

If the ballast is made well it is supposed to be able to handle this untill the lamp fuses

If the ballast is not made well, it can blow at any moment anyway.... Though it is under higher stress when with EOL lamp so have higher chance to be damaged at that time

It is possible for a ballast to have ome initial damage done when 1 lamp EOL'd and then the damage progresses and the ballast only fails a while later (when its allready with the next lamp), but this may as well be just a random failure or as result of a surge in the line

How Ash wrote, both the excessive ballast, as well as the filament stress is caused by exactly the same: Overload of the ballast output circuit (the lamp filament is part of it) caused by worn off electrode emission coat (that is the primary cause).

The filament fusing could in fact only protect the ballast, but it should happen before the ballast get damaged (by the same stress causing the filaments to fuse).
If the filaments are too tough, or the ballast too weak, the ballast get damaged first. The damage does not have to cause the ballast to immediately stop working, but it could damage the components so, the final failure is a matter of few hours of operation (e.g. with the new lamp).

So back to the lamp replacement: Replacing the lamp before the EOL is the only option to really make sure the ballast does not get hurt. It is not, because the fusing filaments would be dangerous, but because the same fault leading to the filament fusing is responsible for the ballast damage as well. So preventing this effect from happening is the way to protect the ballast.
Well, the real practical problem is recognizing when the lamp is going to fail before it actually does so. Usually once the lastr bit of the emission coat get consumed, it is matter of minutes till the filament, or ballast blow out. And before that the lamp still work normally, without any overloading whatsoever (so checking the ballast for signs of overload does not help either).

There are basically only two options:
Either the ballast components are overdesigned so, it could handle the high voltage/current/hard switching condition without any component being overloaded (even thermally; that mean the ballast should be able to deliver at least 2..3x the rated power into the higher-than-rated impedance load still without overheating/overloading of any components),
Or the ballast shall be equipped with a protection circuit shutting it down, before the lamp state and consequent ballast stress reach the limit of what the ballast is able to handle safely.

Although the first seems to have more margin for normal operation, the margin for the lamp EOL is very hard to predict, as the circuit voltages/current could easily vary more than factor of two over normal component tolerances, while it is very hard to predict the actual tolerance corners yielding to the worst case stress. Consequently even when few 10's of test sample ballasts appear robust enough during the validation tests, during production may appear quite a lot of pieces yielding so high fault currents, having too little margin to handle the EOL well. The main risks are the thermal instabilities (tendencies to e.g. thermal runaways or so).
The second approach is way better predictable (the maximum fault current could be kept within +/-20% tolerance, what is quite luxurious to design for), but the protection scheme have be validated against really complete EOL progress (when the ballast only shut down when the arc is interrupted, it is by far not enough to test when validating the design). But when designed well, it become quite immune towards component tolerances, even during unexpected thermal environment - some concepts tend to respond and shut down even when something is overheating,...