However it does not stop them on legal responsibilities for contract breach. That's part of commercial contract agreement and it is part of International Trade law. The one that revoke export license is not US (as component suppliers), but Norway.
There's a legal principle called force majeure. A company is not, in general, legally liable for something which is beyond its control. What exactly is covered by it depends on the laws of the country or countries governing the contract, & the terms of the contract, but if a company is unable to fulfil a contract because of an unexpected & not reasonaby foreseeable legal change in its own country, it usually can't be sued for failure to fulfil it. I would expect it to have to refund any money paid. In this case, I expect Kongsberg will try to sell the missiles to a country which the new restrictions permit, to recover its losses as far as possible.
If Norway cannot allow the export because the USA has changed ITAR restrictions on specific components (I don't know if that's the case), again, that's beyond Norway's control. If the change was expected, it should be possible to sue the Norwegian government, but if it's unexpected, Norway might be able to claim force majeure. Norway's import of components subject to ITAR rules is dependent on Norway complying with US rules. Break them, & the USA could legally & contractually cease all support for, e.g, Norway's F-35s, & much more.
None of this applies to reasonably foreseeable events, such as bad weather, or earthquakes in earthquake-prone regions. One should insure against them, as far as possible.