The thousands of tons of molten lithium needed for useful operation would, if ever exposed to air, prove extremely difficult to put out.

That would be what they might call an "expensive setback".

Molten lithium (or Pb-Li) probably won't be used in magnetic fusion reactors, because the magnetic forces from induced currents in the flowing metal would cause unacceptable pressures to develop. There was hope that insulating coatings for metal structures could be developed to deal with this, but apparently even small cracks are too much.

So, fugure lithium hydride, instead?

They need a great deal of 6Li/7Li in the path of the neutrons to breed fuel. How they would extract small PPB concentration of volatiles is unclear.

A lithium hydride breach would be no picnic, either.

Lithium-containing ceramics, perhaps.

What happens if its exposed to air?

It burns very hot. Also water won't help you.

On other hand amounts used are relatively minor so it isn't massively bad issue.

There are some great videos on YouTube about how alkali metals behave in contact with air or, for extra amusement, water. Those don't generally present superheated, molten alkali metals.