It's the right decision but I doubt that Republican trifectas in Iowa and New Hampshire will just sit idly and relinquish their coveted position in the primary calendar. It will be up to the DNC then to discourage the candidates from campaigning in these states.
For New Hampshire yeah, but aren't the caucuses run by the party?
Correct. The Democratic and Republican Caucuses can simply be held on separate days in IA. This already routinely happens for NV.
For NH, the DNC can simply strip it of its delegates and then it just becomes a non-binding beauty contest. They can hold a caucus or something at some later date, or just not allow NH to vote at the DNC at all.