I don't think it's a good argument. String theory is just "one application" of advanced mathematical physics. It's like saying that software developers specialised in ReactJS would lose their career if ReactJS is suddenly abandoned.

Not a fair comparison because one is exposed to real life market forces vs. academic inertia.

ReactJS devs will retrain when the market dies. Professors still publishing theories/experiments costing large amounts of public monies better spent elsewhere.