PPF should provide adequate protection.
When headlights start to fade, it is because the surface is oxidizing. You can correct this by removing the oxidation with machine polishing (and sanding when needed), but without adding protection, the bare plastic will oxidize again in a short time. Since good PPF (like xpel ultimate) resists oxidation, yellowing, etc. it should help to keep the headlights looking good for longer periods of time.
Would I consider it 'permanent fix'? No... I imagine at some point it will need to be replaced, however Xpel offers a 10 yr warranty against yellowing, cracking, etc.
I'm certainly no expert with PPF, so someone else can certainly chime in. I may be off base.
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